diff --git a/src/background/services/network/NetworkService.test.ts b/src/background/services/network/NetworkService.test.ts
index 11bb456f..b8e0b337 100644
--- a/src/background/services/network/NetworkService.test.ts
+++ b/src/background/services/network/NetworkService.test.ts
@@ -103,6 +103,38 @@ describe('background/services/network/NetworkService', () => {
   const avaxMainnet = mockNetwork(NetworkVMType.EVM, false, {
     chainId: 43114,
   });
+  const leetNetwork = mockNetwork(NetworkVMType.EVM, false, {
+    chainId: 1337,
+  });
+  const btcNetwork = mockNetwork(NetworkVMType.BITCOIN, false, {
+    chainId: ChainId.BITCOIN,
+  });
+  const sepolia = mockNetwork(NetworkVMType.EVM, true, {
+    chainId: 11155111,
+  });
+
+  const mockChainList = (instance: NetworkService) => {
+    // eslint-disable-next-line
+    // @ts-ignore
+    jest.spyOn(instance._rawNetworks, 'promisify').mockResolvedValue(
+      Promise.resolve({
+        [ethMainnet.chainId]: ethMainnet,
+        [avaxMainnet.chainId]: avaxMainnet,
+        [btcNetwork.chainId]: btcNetwork,
+        [leetNetwork.chainId]: leetNetwork,
+        [sepolia.chainId]: sepolia,
+      })
+    );
+    jest.spyOn(instance.allNetworks, 'promisify').mockResolvedValue(
+      Promise.resolve({
+        [ethMainnet.chainId]: ethMainnet,
+        [avaxMainnet.chainId]: avaxMainnet,
+        [btcNetwork.chainId]: btcNetwork,
+        [leetNetwork.chainId]: leetNetwork,
+        [sepolia.chainId]: sepolia,
+      })
+    );
+  };
 
   beforeAll(() => {
     process.env = {
@@ -115,27 +147,10 @@ describe('background/services/network/NetworkService', () => {
   beforeEach(() => {
     jest.resetAllMocks();
 
-    jest.mocked(getChainsAndTokens).mockResolvedValue({
-      [43114]: {
-        chainName: 'test chain',
-        chainId: 123,
-        vmName: NetworkVMType.EVM,
-        rpcUrl: 'https://rpcurl.example',
-        explorerUrl: 'https://explorer.url',
-        networkToken: {
-          name: 'test network token',
-          symbol: 'TNT',
-          description: '',
-          decimals: 18,
-          logoUri: '',
-        },
-        logoUri: '',
-        primaryColor: 'blue',
-        isTestnet: false,
-      },
-    });
+    jest.mocked(getChainsAndTokens).mockResolvedValue({});
 
     jest.mocked(FetchRequest).mockImplementation((url) => ({ url } as any));
+    mockChainList(service);
   });
 
   afterAll(() => {
@@ -143,18 +158,12 @@ describe('background/services/network/NetworkService', () => {
   });
 
   describe('.getInitialNetworkForDapp()', () => {
-    const leetNetwork = mockNetwork(NetworkVMType.EVM, false, {
-      chainId: 1337,
-    });
-    const btcNetwork = mockNetwork(NetworkVMType.BITCOIN, false, {
-      chainId: ChainId.BITCOIN,
-    });
-
     const chainlist = {
       [ethMainnet.chainId]: ethMainnet,
       [avaxMainnet.chainId]: avaxMainnet,
       [leetNetwork.chainId]: leetNetwork,
       [btcNetwork.chainId]: btcNetwork,
+      [sepolia.chainId]: sepolia,
     };
 
     it('returns the most recently active network for given domain', async () => {
@@ -181,7 +190,7 @@ describe('background/services/network/NetworkService', () => {
         .mockResolvedValueOnce(chainlist);
 
       await service.init();
-      await service.setNetwork(runtime.id, leetNetwork);
+      await service.setNetwork(runtime.id, leetNetwork.caipId);
 
       const network = await service.getInitialNetworkForDapp('test.app');
 
@@ -196,7 +205,7 @@ describe('background/services/network/NetworkService', () => {
         .mockResolvedValueOnce(chainlist);
 
       await service.init();
-      await service.setNetwork(runtime.id, btcNetwork);
+      await service.setNetwork(runtime.id, btcNetwork.caipId);
 
       const network = await service.getInitialNetworkForDapp('core.app');
 
@@ -211,7 +220,7 @@ describe('background/services/network/NetworkService', () => {
         .mockResolvedValueOnce(chainlist);
 
       await service.init();
-      await service.setNetwork(runtime.id, btcNetwork);
+      await service.setNetwork(runtime.id, btcNetwork.caipId);
 
       const network = await service.getInitialNetworkForDapp('test.app');
 
@@ -241,7 +250,7 @@ describe('background/services/network/NetworkService', () => {
     });
 
     it('persists current network for given domain', async () => {
-      await service.setNetwork('test.app', ethMainnet);
+      await service.setNetwork('test.app', ethMainnet.caipId);
 
       expect(storageServiceMock.save).toHaveBeenCalledWith(
         NETWORK_STORAGE_KEY,
@@ -258,7 +267,7 @@ describe('background/services/network/NetworkService', () => {
 
       service.dappScopeChanged.addOnce(listener);
 
-      await service.setNetwork('test.app', ethMainnet);
+      await service.setNetwork('test.app', ethMainnet.caipId);
 
       expect(listener).toHaveBeenCalledWith({
         domain: 'test.app',
@@ -267,17 +276,14 @@ describe('background/services/network/NetworkService', () => {
     });
 
     describe('when dApp network switch results in environment change', () => {
-      const sepolia = mockNetwork(NetworkVMType.EVM, true, {
-        chainId: 11155111,
-      });
-
       beforeEach(async () => {
         service = new NetworkService(
           storageServiceMock,
           featureFlagsServiceMock
         );
+        mockChainList(service);
         // Set Ethereum Mainnet directly for the frontend
-        await service.setNetwork(runtime.id, ethMainnet);
+        await service.setNetwork(runtime.id, ethMainnet.caipId);
         expect(service.uiActiveNetwork).toEqual(ethMainnet);
       });
 
@@ -285,7 +291,7 @@ describe('background/services/network/NetworkService', () => {
         storageServiceMock.load.mockResolvedValueOnce({
           [runtime.id]: sepolia.caipId,
         });
-        await service.setNetwork('app.uniswap.io', sepolia);
+        await service.setNetwork('app.uniswap.io', sepolia.caipId);
         expect(storageServiceMock.save).toHaveBeenCalledWith(
           NETWORK_STORAGE_KEY,
           expect.objectContaining({
@@ -300,7 +306,7 @@ describe('background/services/network/NetworkService', () => {
         storageServiceMock.load.mockResolvedValueOnce({
           [runtime.id]: sepolia.caipId,
         });
-        await service.setNetwork('app.uniswap.io', sepolia);
+        await service.setNetwork('app.uniswap.io', sepolia.caipId);
         expect(service.uiActiveNetwork).toEqual(sepolia);
         expect(storageServiceMock.save).toHaveBeenCalledWith(
           NETWORK_STORAGE_KEY,
@@ -318,7 +324,7 @@ describe('background/services/network/NetworkService', () => {
 
         service.developerModeChanged.addOnce(onDevModeChange);
 
-        await service.setNetwork('app.uniswap.io', sepolia);
+        await service.setNetwork('app.uniswap.io', sepolia.caipId);
         expect(service.uiActiveNetwork).toEqual(sepolia);
 
         expect(onDevModeChange).toHaveBeenCalledWith(true);
@@ -327,7 +333,7 @@ describe('background/services/network/NetworkService', () => {
 
     describe('when changing network for synchronized dApps', () => {
       it('uses the extension ID as domain', async () => {
-        await service.setNetwork('core.app', ethMainnet);
+        await service.setNetwork('core.app', ethMainnet.caipId);
 
         expect(storageServiceMock.save).toHaveBeenCalledWith(
           NETWORK_STORAGE_KEY,
@@ -340,12 +346,18 @@ describe('background/services/network/NetworkService', () => {
       });
 
       it('changes the network for the extension ui as well', async () => {
+        jest.spyOn(service.allNetworks, 'promisify').mockResolvedValue(
+          Promise.resolve({
+            [ethMainnet.chainId]: ethMainnet,
+            [avaxMainnet.chainId]: avaxMainnet,
+          })
+        );
         // Set Ethereum directly for the frontend
-        await service.setNetwork(runtime.id, ethMainnet);
+        await service.setNetwork(runtime.id, ethMainnet.caipId);
         expect(service.uiActiveNetwork).toEqual(ethMainnet);
 
         // Set C-Chain for core.app and expect it to change also for the extension UI
-        await service.setNetwork('core.app', avaxMainnet);
+        await service.setNetwork('core.app', avaxMainnet.caipId);
         expect(service.uiActiveNetwork).toEqual(avaxMainnet);
       });
 
@@ -353,8 +365,13 @@ describe('background/services/network/NetworkService', () => {
         const listener = jest.fn();
 
         service.dappScopeChanged.addOnce(listener);
+        jest.spyOn(service.allNetworks, 'promisify').mockResolvedValue(
+          Promise.resolve({
+            [ethMainnet.chainId]: ethMainnet,
+          })
+        );
 
-        await service.setNetwork('core.app', ethMainnet);
+        await service.setNetwork('core.app', ethMainnet.caipId);
 
         expect(listener).toHaveBeenCalledWith({
           domain: runtime.id,
@@ -373,6 +390,7 @@ describe('background/services/network/NetworkService', () => {
     it('saves custom RPC headers', async () => {
       const overrides = {
         chainId: 1337,
+        caipId: 'eip155:1337',
         customRpcHeaders: {
           'X-Glacier-Api-Key': 'my-elite-api-key',
         },
@@ -415,8 +433,13 @@ describe('background/services/network/NetworkService', () => {
       jest.spyOn(networkService._rawNetworks, 'promisify').mockResolvedValue({
         1337: activeNetwork,
       });
+      jest.spyOn(networkService.allNetworks, 'promisify').mockResolvedValue(
+        Promise.resolve({
+          1337: activeNetwork,
+        })
+      );
 
-      await networkService.setNetwork(runtime.id, activeNetwork);
+      await networkService.setNetwork(runtime.id, activeNetwork.caipId);
 
       await networkService.updateNetworkOverrides({
         caipId: 'eip155:1337',
@@ -437,24 +460,25 @@ describe('background/services/network/NetworkService', () => {
   describe('saveCustomNetwork()', () => {
     let customNetwork;
 
-    beforeEach(() => {
+    beforeEach(async () => {
       customNetwork = mockNetwork(NetworkVMType.EVM, false);
     });
 
     it('should throw an error because of the chainlist failed to load', async () => {
       jest
         // eslint-disable-next-line
-        // @ts-expect-error
+        // @ts-ignore
         .spyOn(service._rawNetworks, 'promisify')
-        .mockResolvedValue(Promise.resolve(undefined));
-      expect(service.saveCustomNetwork(customNetwork)).rejects.toThrow(
+        .mockResolvedValueOnce(Promise.resolve(undefined));
+
+      await expect(service.saveCustomNetwork(customNetwork)).rejects.toThrow(
         'chainlist failed to load'
       );
     });
 
     it('should throw an error because of duplicated ID', async () => {
       const newCustomNetwork = { ...customNetwork, chainId: 43114 };
-      expect(service.saveCustomNetwork(newCustomNetwork)).rejects.toThrow(
+      await expect(service.saveCustomNetwork(newCustomNetwork)).rejects.toThrow(
         'chain ID already exists'
       );
     });
@@ -476,11 +500,8 @@ describe('background/services/network/NetworkService', () => {
         ...customNetwork,
         rpcUrl: newRpcUrl,
       };
-      await service.saveCustomNetwork(newCustomNetwork);
-
-      // Set it as active
-      const savedActiveNetwork = await service.getNetwork(
-        newCustomNetwork.chainId
+      const savedActiveNetwork = await service.saveCustomNetwork(
+        newCustomNetwork
       );
 
       expect(savedActiveNetwork?.rpcUrl).toBe(newRpcUrl);
diff --git a/src/background/services/network/NetworkService.ts b/src/background/services/network/NetworkService.ts
index 2e80240a..8680a17c 100644
--- a/src/background/services/network/NetworkService.ts
+++ b/src/background/services/network/NetworkService.ts
@@ -149,18 +149,25 @@ export class NetworkService implements OnLock, OnStorageReady {
     );
   }
 
-  async setNetwork(domain: string, selectedNetwork: NetworkWithCaipId) {
+  async setNetwork(domain: string, caipId: string) {
     const isSynced = isSyncDomain(domain);
+    // For supported networks, use config from saved chainlist
+    // instead of relying on payload that may come from a 3rd party:
+    const targetNetwork = await this.getNetwork(caipId);
+    if (!targetNetwork) {
+      throw new Error(`Network not found: ${caipId}`);
+    }
+
     const changesEnvironment =
       Boolean(this._uiActiveNetwork?.isTestnet) !==
-      Boolean(selectedNetwork.isTestnet);
+      Boolean(targetNetwork.isTestnet);
 
     if (isSynced || changesEnvironment) {
-      this.uiActiveNetwork = selectedNetwork;
+      this.uiActiveNetwork = targetNetwork;
     }
 
     // Save scope for requesting dApp
-    await this.#updateDappScopes({ [domain]: selectedNetwork.caipId });
+    await this.#updateDappScopes({ [domain]: targetNetwork.caipId });
 
     // If change resulted in an environment switch, also notify other dApps
     if (changesEnvironment) {
@@ -173,7 +180,7 @@ export class NetworkService implements OnLock, OnStorageReady {
           .map(([savedDomain]) => [
             savedDomain,
             chainIdToCaip(
-              selectedNetwork.isTestnet
+              targetNetwork.isTestnet
                 ? ChainId.AVALANCHE_TESTNET_ID
                 : ChainId.AVALANCHE_MAINNET_ID
             ),
@@ -679,7 +686,7 @@ export class NetworkService implements OnLock, OnStorageReady {
       );
 
       if (network) {
-        await this.setNetwork(runtime.id, network);
+        await this.setNetwork(runtime.id, network.caipId);
       }
     }
 
diff --git a/src/background/services/network/handlers/avalanche_setDeveloperMode.ts b/src/background/services/network/handlers/avalanche_setDeveloperMode.ts
index 83b81df7..c89e7948 100644
--- a/src/background/services/network/handlers/avalanche_setDeveloperMode.ts
+++ b/src/background/services/network/handlers/avalanche_setDeveloperMode.ts
@@ -7,6 +7,7 @@ import { NetworkService } from '../NetworkService';
 import { ethErrors } from 'eth-rpc-errors';
 import { openApprovalWindow } from '@src/background/runtime/openApprovalWindow';
 import { ChainId } from '@avalabs/core-chains-sdk';
+import { chainIdToCaip } from '@src/utils/caipConversion';
 
 @injectable()
 export class AvalancheSetDeveloperModeHandler extends DAppRequestHandler {
@@ -71,16 +72,15 @@ export class AvalancheSetDeveloperModeHandler extends DAppRequestHandler {
         throw new Error('Unrecognized domain');
       }
 
-      const network = await this.networkService.getNetwork(
-        isTestmode ? ChainId.AVALANCHE_TESTNET_ID : ChainId.AVALANCHE_MAINNET_ID
+      await this.networkService.setNetwork(
+        domain,
+        chainIdToCaip(
+          isTestmode
+            ? ChainId.AVALANCHE_TESTNET_ID
+            : ChainId.AVALANCHE_MAINNET_ID
+        )
       );
 
-      if (!network) {
-        throw new Error('Target network not found');
-      }
-
-      await this.networkService.setNetwork(domain, network);
-
       onSuccess(null);
     } catch (e) {
       onError(e);
diff --git a/src/background/services/network/handlers/saveCustomNetwork.ts b/src/background/services/network/handlers/saveCustomNetwork.ts
index 492c706e..aeb56499 100644
--- a/src/background/services/network/handlers/saveCustomNetwork.ts
+++ b/src/background/services/network/handlers/saveCustomNetwork.ts
@@ -1,10 +1,10 @@
 import { ExtensionRequest } from '@src/background/connections/extensionConnection/models';
 import { ExtensionRequestHandler } from '@src/background/connections/models';
-import { resolve } from '@src/utils/promiseResolver';
 import { injectable } from 'tsyringe';
 import { NetworkService } from '../NetworkService';
 import { CustomNetworkPayload } from '../models';
 import { runtime } from 'webextension-polyfill';
+import { resolve } from '@avalabs/core-utils-sdk';
 
 type HandlerType = ExtensionRequestHandler<
   ExtensionRequest.NETWORK_SAVE_CUSTOM,
@@ -43,14 +43,14 @@ export class SaveCustomNetworkHandler implements HandlerType {
       this.networkService.saveCustomNetwork(network)
     );
 
-    if (err) {
+    if (err || !addedNetwork) {
       return {
         ...request,
-        error: err.toString(),
+        error: err?.toString() ?? 'Adding custom network failed',
       };
     }
 
-    await this.networkService.setNetwork(runtime.id, addedNetwork);
+    await this.networkService.setNetwork(runtime.id, addedNetwork.caipId);
 
     return {
       ...request,
diff --git a/src/background/services/network/handlers/setActiveNetwork.ts b/src/background/services/network/handlers/setActiveNetwork.ts
index fb4ec53d..a351326c 100644
--- a/src/background/services/network/handlers/setActiveNetwork.ts
+++ b/src/background/services/network/handlers/setActiveNetwork.ts
@@ -21,19 +21,8 @@ export class SetActiveNetworkHandler implements HandlerType {
 
   handle: HandlerType['handle'] = async ({ request }) => {
     const [scope] = request.params;
-    const [network, networkErr] = await resolve(
-      this.networkService.getNetwork(scope)
-    );
-
-    if (networkErr || !network) {
-      return {
-        ...request,
-        error: 'Ttarget network not found',
-      };
-    }
-
     const [, err] = await resolve(
-      this.networkService.setNetwork(runtime.id, network)
+      this.networkService.setNetwork(runtime.id, scope)
     );
 
     if (err) {
diff --git a/src/background/services/network/handlers/setDeveloperMode.ts b/src/background/services/network/handlers/setDeveloperMode.ts
index 5c2f9564..2cbe146b 100644
--- a/src/background/services/network/handlers/setDeveloperMode.ts
+++ b/src/background/services/network/handlers/setDeveloperMode.ts
@@ -7,6 +7,7 @@ import { ExtensionRequestHandler } from '@src/background/connections/models';
 import { resolve } from '@src/utils/promiseResolver';
 
 import { NetworkService } from '../NetworkService';
+import { chainIdToCaip } from '@src/utils/caipConversion';
 
 type HandlerType = ExtensionRequestHandler<
   ExtensionRequest.NETWORK_SET_DEVELOPER_MODE,
@@ -22,19 +23,15 @@ export class SetDevelopermodeNetworkHandler implements HandlerType {
 
   handle: HandlerType['handle'] = async ({ request }) => {
     const [enableDeveloperMode] = request.params;
-
-    const network = await this.networkService.getNetwork(
-      enableDeveloperMode
-        ? ChainId.AVALANCHE_TESTNET_ID
-        : ChainId.AVALANCHE_MAINNET_ID
-    );
-
-    if (!network) {
-      throw new Error('Target network not found');
-    }
-
     const [, err] = await resolve(
-      this.networkService.setNetwork(runtime.id, network)
+      this.networkService.setNetwork(
+        runtime.id,
+        chainIdToCaip(
+          enableDeveloperMode
+            ? ChainId.AVALANCHE_TESTNET_ID
+            : ChainId.AVALANCHE_MAINNET_ID
+        )
+      )
     );
 
     if (err) {
diff --git a/src/background/services/network/handlers/wallet_addEthereumChain.test.ts b/src/background/services/network/handlers/wallet_addEthereumChain.test.ts
index 2832ab46..23cbc659 100644
--- a/src/background/services/network/handlers/wallet_addEthereumChain.test.ts
+++ b/src/background/services/network/handlers/wallet_addEthereumChain.test.ts
@@ -568,9 +568,7 @@ describe('background/services/network/handlers/wallet_addEthereumChain.ts', () =
     expect(mockNetworkService.setNetwork).toHaveBeenCalledTimes(1);
     expect(mockNetworkService.setNetwork).toHaveBeenCalledWith(
       'core.app',
-      expect.objectContaining({
-        chainId: 43113,
-      })
+      'eip155:43113'
     );
   });
 
@@ -787,7 +785,7 @@ describe('background/services/network/handlers/wallet_addEthereumChain.ts', () =
 
       expect(mockNetworkService.setNetwork).toHaveBeenCalledWith(
         mockPendingAction.site?.domain,
-        mockPendingAction.displayData.network
+        mockPendingAction.displayData.network.caipId
       );
       expect(mockNetworkService.saveCustomNetwork).toHaveBeenCalledTimes(1);
       expect(mockNetworkService.saveCustomNetwork).toHaveBeenCalledWith({
@@ -830,6 +828,7 @@ describe('background/services/network/handlers/wallet_addEthereumChain.ts', () =
       const network = {
         ...mockPendingAction.displayData.network,
         chainId: 43113,
+        caipId: 'eip155:43113',
       };
 
       await handler.onActionApproved(
@@ -850,7 +849,7 @@ describe('background/services/network/handlers/wallet_addEthereumChain.ts', () =
       expect(mockNetworkService.saveCustomNetwork).not.toHaveBeenCalled();
       expect(mockNetworkService.setNetwork).toHaveBeenCalledWith(
         mockPendingAction.site?.domain,
-        network
+        network.caipId
       );
 
       expect(successHandler).toHaveBeenCalledTimes(1);
@@ -873,6 +872,7 @@ describe('background/services/network/handlers/wallet_addEthereumChain.ts', () =
             network: {
               ...mockPendingAction.displayData.network,
               chainId: 43113,
+              caipId: 'eip155:43113',
             },
             options: {
               requiresGlacierApiKey: false,
diff --git a/src/background/services/network/handlers/wallet_addEthereumChain.ts b/src/background/services/network/handlers/wallet_addEthereumChain.ts
index 0cbb5af4..15fbcec3 100644
--- a/src/background/services/network/handlers/wallet_addEthereumChain.ts
+++ b/src/background/services/network/handlers/wallet_addEthereumChain.ts
@@ -188,7 +188,7 @@ export class WalletAddEthereumChainHandler extends DAppRequestHandler {
       await this.networkService.saveCustomNetwork(network);
     }
 
-    await this.networkService.setNetwork(domain, network);
+    await this.networkService.setNetwork(domain, network.caipId);
   }
 
   onActionApproved = async (
diff --git a/src/background/services/network/handlers/wallet_switchEthereumChain.ts b/src/background/services/network/handlers/wallet_switchEthereumChain.ts
index c376ab76..58e79c91 100644
--- a/src/background/services/network/handlers/wallet_switchEthereumChain.ts
+++ b/src/background/services/network/handlers/wallet_switchEthereumChain.ts
@@ -55,7 +55,7 @@ export class WalletSwitchEthereumChainHandler extends DAppRequestHandler {
       if (skipApproval) {
         await this.networkService.setNetwork(
           request.site.domain,
-          supportedNetwork
+          supportedNetwork.caipId
         );
         return { ...request, result: null };
       }
@@ -98,7 +98,7 @@ export class WalletSwitchEthereumChainHandler extends DAppRequestHandler {
     try {
       await this.networkService.setNetwork(
         pendingAction.site.domain,
-        pendingAction.displayData.network
+        pendingAction.displayData.network.caipId
       );
 
       onSuccess(null);
diff --git a/src/background/services/onboarding/finalizeOnboarding.ts b/src/background/services/onboarding/finalizeOnboarding.ts
index 0f778972..c4341418 100644
--- a/src/background/services/onboarding/finalizeOnboarding.ts
+++ b/src/background/services/onboarding/finalizeOnboarding.ts
@@ -26,10 +26,8 @@ export async function finalizeOnboarding({
   await networkService.addFavoriteNetwork(ChainId.BITCOIN);
   await networkService.addFavoriteNetwork(ChainId.ETHEREUM_HOMESTEAD);
 
-  await networkService.setNetwork(
-    runtime.id,
-    await networkService.getAvalancheNetwork()
-  );
+  const cChain = await networkService.getAvalancheNetwork();
+  await networkService.setNetwork(runtime.id, cChain.caipId);
 
   const allAccounts = accountsService.getAccounts();
   const addedAccounts = allAccounts.primary[walletId];