diff --git a/modules/openapi-generator/src/main/resources/swift5/libraries/urlsession/URLSessionImplementations.mustache b/modules/openapi-generator/src/main/resources/swift5/libraries/urlsession/URLSessionImplementations.mustache
index b045c18c66b56..d09015f346b93 100644
--- a/modules/openapi-generator/src/main/resources/swift5/libraries/urlsession/URLSessionImplementations.mustache
+++ b/modules/openapi-generator/src/main/resources/swift5/libraries/urlsession/URLSessionImplementations.mustache
@@ -611,12 +611,24 @@ private class FormURLEncoding: ParameterEncoding {
         var urlRequest = urlRequest
 
         var requestBodyComponents = URLComponents()
-        requestBodyComponents.queryItems = APIHelper.mapValuesToQueryItems(parameters ?? [:])
+        let queryItems = APIHelper.mapValuesToQueryItems(parameters ?? [:])
+        
+        /// `httpBody` needs to be percent encoded
+        /// -> https://developer.mozilla.org/en-US/docs/Web/HTTP/Methods/POST
+        /// "application/x-www-form-urlencoded: [...] Non-alphanumeric characters in both keys and values are percent-encoded"
+        let percentEncodedQueryItems = queryItems?.compactMap { queryItem in
+            return URLQueryItem(
+                name: queryItem.name.addingPercentEncoding(withAllowedCharacters: .alphanumerics) ?? queryItem.name,
+                value: queryItem.value?.addingPercentEncoding(withAllowedCharacters: .alphanumerics))
+        }
+        requestBodyComponents.queryItems = percentEncodedQueryItems
 
         if urlRequest.value(forHTTPHeaderField: "Content-Type") == nil {
             urlRequest.setValue("application/x-www-form-urlencoded", forHTTPHeaderField: "Content-Type")
         }
 
+        /// We can't use `requestBodyComponents.percentEncodedQuery` since this does NOT percent encode the `+` sign
+        /// that is why we do the percent encoding manually for each key/value pair
         urlRequest.httpBody = requestBodyComponents.query?.data(using: .utf8)
 
         return urlRequest
diff --git a/samples/client/petstore/swift5/asyncAwaitLibrary/PetstoreClient/Classes/OpenAPIs/URLSessionImplementations.swift b/samples/client/petstore/swift5/asyncAwaitLibrary/PetstoreClient/Classes/OpenAPIs/URLSessionImplementations.swift
index 6fa4d0e20eb9b..15616ae3028d2 100644
--- a/samples/client/petstore/swift5/asyncAwaitLibrary/PetstoreClient/Classes/OpenAPIs/URLSessionImplementations.swift
+++ b/samples/client/petstore/swift5/asyncAwaitLibrary/PetstoreClient/Classes/OpenAPIs/URLSessionImplementations.swift
@@ -611,12 +611,24 @@ private class FormURLEncoding: ParameterEncoding {
         var urlRequest = urlRequest
 
         var requestBodyComponents = URLComponents()
-        requestBodyComponents.queryItems = APIHelper.mapValuesToQueryItems(parameters ?? [:])
+        let queryItems = APIHelper.mapValuesToQueryItems(parameters ?? [:])
+        
+        /// `httpBody` needs to be percent encoded
+        /// -> https://developer.mozilla.org/en-US/docs/Web/HTTP/Methods/POST
+        /// "application/x-www-form-urlencoded: [...] Non-alphanumeric characters in both keys and values are percent-encoded"
+        let percentEncodedQueryItems = queryItems?.compactMap { queryItem in
+            return URLQueryItem(
+                name: queryItem.name.addingPercentEncoding(withAllowedCharacters: .alphanumerics) ?? queryItem.name,
+                value: queryItem.value?.addingPercentEncoding(withAllowedCharacters: .alphanumerics))
+        }
+        requestBodyComponents.queryItems = percentEncodedQueryItems
 
         if urlRequest.value(forHTTPHeaderField: "Content-Type") == nil {
             urlRequest.setValue("application/x-www-form-urlencoded", forHTTPHeaderField: "Content-Type")
         }
 
+        /// We can't use `requestBodyComponents.percentEncodedQuery` since this does NOT percent encode the `+` sign
+        /// that is why we do the percent encoding manually for each key/value pair
         urlRequest.httpBody = requestBodyComponents.query?.data(using: .utf8)
 
         return urlRequest
diff --git a/samples/client/petstore/swift5/combineLibrary/PetstoreClient/Classes/OpenAPIs/URLSessionImplementations.swift b/samples/client/petstore/swift5/combineLibrary/PetstoreClient/Classes/OpenAPIs/URLSessionImplementations.swift
index 6fa4d0e20eb9b..15616ae3028d2 100644
--- a/samples/client/petstore/swift5/combineLibrary/PetstoreClient/Classes/OpenAPIs/URLSessionImplementations.swift
+++ b/samples/client/petstore/swift5/combineLibrary/PetstoreClient/Classes/OpenAPIs/URLSessionImplementations.swift
@@ -611,12 +611,24 @@ private class FormURLEncoding: ParameterEncoding {
         var urlRequest = urlRequest
 
         var requestBodyComponents = URLComponents()
-        requestBodyComponents.queryItems = APIHelper.mapValuesToQueryItems(parameters ?? [:])
+        let queryItems = APIHelper.mapValuesToQueryItems(parameters ?? [:])
+        
+        /// `httpBody` needs to be percent encoded
+        /// -> https://developer.mozilla.org/en-US/docs/Web/HTTP/Methods/POST
+        /// "application/x-www-form-urlencoded: [...] Non-alphanumeric characters in both keys and values are percent-encoded"
+        let percentEncodedQueryItems = queryItems?.compactMap { queryItem in
+            return URLQueryItem(
+                name: queryItem.name.addingPercentEncoding(withAllowedCharacters: .alphanumerics) ?? queryItem.name,
+                value: queryItem.value?.addingPercentEncoding(withAllowedCharacters: .alphanumerics))
+        }
+        requestBodyComponents.queryItems = percentEncodedQueryItems
 
         if urlRequest.value(forHTTPHeaderField: "Content-Type") == nil {
             urlRequest.setValue("application/x-www-form-urlencoded", forHTTPHeaderField: "Content-Type")
         }
 
+        /// We can't use `requestBodyComponents.percentEncodedQuery` since this does NOT percent encode the `+` sign
+        /// that is why we do the percent encoding manually for each key/value pair
         urlRequest.httpBody = requestBodyComponents.query?.data(using: .utf8)
 
         return urlRequest
diff --git a/samples/client/petstore/swift5/default/PetstoreClient/Classes/OpenAPIs/URLSessionImplementations.swift b/samples/client/petstore/swift5/default/PetstoreClient/Classes/OpenAPIs/URLSessionImplementations.swift
index 6fa4d0e20eb9b..15616ae3028d2 100644
--- a/samples/client/petstore/swift5/default/PetstoreClient/Classes/OpenAPIs/URLSessionImplementations.swift
+++ b/samples/client/petstore/swift5/default/PetstoreClient/Classes/OpenAPIs/URLSessionImplementations.swift
@@ -611,12 +611,24 @@ private class FormURLEncoding: ParameterEncoding {
         var urlRequest = urlRequest
 
         var requestBodyComponents = URLComponents()
-        requestBodyComponents.queryItems = APIHelper.mapValuesToQueryItems(parameters ?? [:])
+        let queryItems = APIHelper.mapValuesToQueryItems(parameters ?? [:])
+        
+        /// `httpBody` needs to be percent encoded
+        /// -> https://developer.mozilla.org/en-US/docs/Web/HTTP/Methods/POST
+        /// "application/x-www-form-urlencoded: [...] Non-alphanumeric characters in both keys and values are percent-encoded"
+        let percentEncodedQueryItems = queryItems?.compactMap { queryItem in
+            return URLQueryItem(
+                name: queryItem.name.addingPercentEncoding(withAllowedCharacters: .alphanumerics) ?? queryItem.name,
+                value: queryItem.value?.addingPercentEncoding(withAllowedCharacters: .alphanumerics))
+        }
+        requestBodyComponents.queryItems = percentEncodedQueryItems
 
         if urlRequest.value(forHTTPHeaderField: "Content-Type") == nil {
             urlRequest.setValue("application/x-www-form-urlencoded", forHTTPHeaderField: "Content-Type")
         }
 
+        /// We can't use `requestBodyComponents.percentEncodedQuery` since this does NOT percent encode the `+` sign
+        /// that is why we do the percent encoding manually for each key/value pair
         urlRequest.httpBody = requestBodyComponents.query?.data(using: .utf8)
 
         return urlRequest
diff --git a/samples/client/petstore/swift5/objcCompatible/PetstoreClient/Classes/OpenAPIs/URLSessionImplementations.swift b/samples/client/petstore/swift5/objcCompatible/PetstoreClient/Classes/OpenAPIs/URLSessionImplementations.swift
index 6fa4d0e20eb9b..15616ae3028d2 100644
--- a/samples/client/petstore/swift5/objcCompatible/PetstoreClient/Classes/OpenAPIs/URLSessionImplementations.swift
+++ b/samples/client/petstore/swift5/objcCompatible/PetstoreClient/Classes/OpenAPIs/URLSessionImplementations.swift
@@ -611,12 +611,24 @@ private class FormURLEncoding: ParameterEncoding {
         var urlRequest = urlRequest
 
         var requestBodyComponents = URLComponents()
-        requestBodyComponents.queryItems = APIHelper.mapValuesToQueryItems(parameters ?? [:])
+        let queryItems = APIHelper.mapValuesToQueryItems(parameters ?? [:])
+        
+        /// `httpBody` needs to be percent encoded
+        /// -> https://developer.mozilla.org/en-US/docs/Web/HTTP/Methods/POST
+        /// "application/x-www-form-urlencoded: [...] Non-alphanumeric characters in both keys and values are percent-encoded"
+        let percentEncodedQueryItems = queryItems?.compactMap { queryItem in
+            return URLQueryItem(
+                name: queryItem.name.addingPercentEncoding(withAllowedCharacters: .alphanumerics) ?? queryItem.name,
+                value: queryItem.value?.addingPercentEncoding(withAllowedCharacters: .alphanumerics))
+        }
+        requestBodyComponents.queryItems = percentEncodedQueryItems
 
         if urlRequest.value(forHTTPHeaderField: "Content-Type") == nil {
             urlRequest.setValue("application/x-www-form-urlencoded", forHTTPHeaderField: "Content-Type")
         }
 
+        /// We can't use `requestBodyComponents.percentEncodedQuery` since this does NOT percent encode the `+` sign
+        /// that is why we do the percent encoding manually for each key/value pair
         urlRequest.httpBody = requestBodyComponents.query?.data(using: .utf8)
 
         return urlRequest
diff --git a/samples/client/petstore/swift5/oneOf/PetstoreClient/Classes/OpenAPIs/URLSessionImplementations.swift b/samples/client/petstore/swift5/oneOf/PetstoreClient/Classes/OpenAPIs/URLSessionImplementations.swift
index 6fa4d0e20eb9b..15616ae3028d2 100644
--- a/samples/client/petstore/swift5/oneOf/PetstoreClient/Classes/OpenAPIs/URLSessionImplementations.swift
+++ b/samples/client/petstore/swift5/oneOf/PetstoreClient/Classes/OpenAPIs/URLSessionImplementations.swift
@@ -611,12 +611,24 @@ private class FormURLEncoding: ParameterEncoding {
         var urlRequest = urlRequest
 
         var requestBodyComponents = URLComponents()
-        requestBodyComponents.queryItems = APIHelper.mapValuesToQueryItems(parameters ?? [:])
+        let queryItems = APIHelper.mapValuesToQueryItems(parameters ?? [:])
+        
+        /// `httpBody` needs to be percent encoded
+        /// -> https://developer.mozilla.org/en-US/docs/Web/HTTP/Methods/POST
+        /// "application/x-www-form-urlencoded: [...] Non-alphanumeric characters in both keys and values are percent-encoded"
+        let percentEncodedQueryItems = queryItems?.compactMap { queryItem in
+            return URLQueryItem(
+                name: queryItem.name.addingPercentEncoding(withAllowedCharacters: .alphanumerics) ?? queryItem.name,
+                value: queryItem.value?.addingPercentEncoding(withAllowedCharacters: .alphanumerics))
+        }
+        requestBodyComponents.queryItems = percentEncodedQueryItems
 
         if urlRequest.value(forHTTPHeaderField: "Content-Type") == nil {
             urlRequest.setValue("application/x-www-form-urlencoded", forHTTPHeaderField: "Content-Type")
         }
 
+        /// We can't use `requestBodyComponents.percentEncodedQuery` since this does NOT percent encode the `+` sign
+        /// that is why we do the percent encoding manually for each key/value pair
         urlRequest.httpBody = requestBodyComponents.query?.data(using: .utf8)
 
         return urlRequest
diff --git a/samples/client/petstore/swift5/promisekitLibrary/PetstoreClient/Classes/OpenAPIs/URLSessionImplementations.swift b/samples/client/petstore/swift5/promisekitLibrary/PetstoreClient/Classes/OpenAPIs/URLSessionImplementations.swift
index 6fa4d0e20eb9b..15616ae3028d2 100644
--- a/samples/client/petstore/swift5/promisekitLibrary/PetstoreClient/Classes/OpenAPIs/URLSessionImplementations.swift
+++ b/samples/client/petstore/swift5/promisekitLibrary/PetstoreClient/Classes/OpenAPIs/URLSessionImplementations.swift
@@ -611,12 +611,24 @@ private class FormURLEncoding: ParameterEncoding {
         var urlRequest = urlRequest
 
         var requestBodyComponents = URLComponents()
-        requestBodyComponents.queryItems = APIHelper.mapValuesToQueryItems(parameters ?? [:])
+        let queryItems = APIHelper.mapValuesToQueryItems(parameters ?? [:])
+        
+        /// `httpBody` needs to be percent encoded
+        /// -> https://developer.mozilla.org/en-US/docs/Web/HTTP/Methods/POST
+        /// "application/x-www-form-urlencoded: [...] Non-alphanumeric characters in both keys and values are percent-encoded"
+        let percentEncodedQueryItems = queryItems?.compactMap { queryItem in
+            return URLQueryItem(
+                name: queryItem.name.addingPercentEncoding(withAllowedCharacters: .alphanumerics) ?? queryItem.name,
+                value: queryItem.value?.addingPercentEncoding(withAllowedCharacters: .alphanumerics))
+        }
+        requestBodyComponents.queryItems = percentEncodedQueryItems
 
         if urlRequest.value(forHTTPHeaderField: "Content-Type") == nil {
             urlRequest.setValue("application/x-www-form-urlencoded", forHTTPHeaderField: "Content-Type")
         }
 
+        /// We can't use `requestBodyComponents.percentEncodedQuery` since this does NOT percent encode the `+` sign
+        /// that is why we do the percent encoding manually for each key/value pair
         urlRequest.httpBody = requestBodyComponents.query?.data(using: .utf8)
 
         return urlRequest
diff --git a/samples/client/petstore/swift5/resultLibrary/PetstoreClient/Classes/OpenAPIs/URLSessionImplementations.swift b/samples/client/petstore/swift5/resultLibrary/PetstoreClient/Classes/OpenAPIs/URLSessionImplementations.swift
index a76ea20537dd3..0f27b0b30eac0 100644
--- a/samples/client/petstore/swift5/resultLibrary/PetstoreClient/Classes/OpenAPIs/URLSessionImplementations.swift
+++ b/samples/client/petstore/swift5/resultLibrary/PetstoreClient/Classes/OpenAPIs/URLSessionImplementations.swift
@@ -611,12 +611,24 @@ private class FormURLEncoding: ParameterEncoding {
         var urlRequest = urlRequest
 
         var requestBodyComponents = URLComponents()
-        requestBodyComponents.queryItems = APIHelper.mapValuesToQueryItems(parameters ?? [:])
+        let queryItems = APIHelper.mapValuesToQueryItems(parameters ?? [:])
+        
+        /// `httpBody` needs to be percent encoded
+        /// -> https://developer.mozilla.org/en-US/docs/Web/HTTP/Methods/POST
+        /// "application/x-www-form-urlencoded: [...] Non-alphanumeric characters in both keys and values are percent-encoded"
+        let percentEncodedQueryItems = queryItems?.compactMap { queryItem in
+            return URLQueryItem(
+                name: queryItem.name.addingPercentEncoding(withAllowedCharacters: .alphanumerics) ?? queryItem.name,
+                value: queryItem.value?.addingPercentEncoding(withAllowedCharacters: .alphanumerics))
+        }
+        requestBodyComponents.queryItems = percentEncodedQueryItems
 
         if urlRequest.value(forHTTPHeaderField: "Content-Type") == nil {
             urlRequest.setValue("application/x-www-form-urlencoded", forHTTPHeaderField: "Content-Type")
         }
 
+        /// We can't use `requestBodyComponents.percentEncodedQuery` since this does NOT percent encode the `+` sign
+        /// that is why we do the percent encoding manually for each key/value pair
         urlRequest.httpBody = requestBodyComponents.query?.data(using: .utf8)
 
         return urlRequest
diff --git a/samples/client/petstore/swift5/rxswiftLibrary/PetstoreClient/Classes/OpenAPIs/URLSessionImplementations.swift b/samples/client/petstore/swift5/rxswiftLibrary/PetstoreClient/Classes/OpenAPIs/URLSessionImplementations.swift
index 6fa4d0e20eb9b..15616ae3028d2 100644
--- a/samples/client/petstore/swift5/rxswiftLibrary/PetstoreClient/Classes/OpenAPIs/URLSessionImplementations.swift
+++ b/samples/client/petstore/swift5/rxswiftLibrary/PetstoreClient/Classes/OpenAPIs/URLSessionImplementations.swift
@@ -611,12 +611,24 @@ private class FormURLEncoding: ParameterEncoding {
         var urlRequest = urlRequest
 
         var requestBodyComponents = URLComponents()
-        requestBodyComponents.queryItems = APIHelper.mapValuesToQueryItems(parameters ?? [:])
+        let queryItems = APIHelper.mapValuesToQueryItems(parameters ?? [:])
+        
+        /// `httpBody` needs to be percent encoded
+        /// -> https://developer.mozilla.org/en-US/docs/Web/HTTP/Methods/POST
+        /// "application/x-www-form-urlencoded: [...] Non-alphanumeric characters in both keys and values are percent-encoded"
+        let percentEncodedQueryItems = queryItems?.compactMap { queryItem in
+            return URLQueryItem(
+                name: queryItem.name.addingPercentEncoding(withAllowedCharacters: .alphanumerics) ?? queryItem.name,
+                value: queryItem.value?.addingPercentEncoding(withAllowedCharacters: .alphanumerics))
+        }
+        requestBodyComponents.queryItems = percentEncodedQueryItems
 
         if urlRequest.value(forHTTPHeaderField: "Content-Type") == nil {
             urlRequest.setValue("application/x-www-form-urlencoded", forHTTPHeaderField: "Content-Type")
         }
 
+        /// We can't use `requestBodyComponents.percentEncodedQuery` since this does NOT percent encode the `+` sign
+        /// that is why we do the percent encoding manually for each key/value pair
         urlRequest.httpBody = requestBodyComponents.query?.data(using: .utf8)
 
         return urlRequest
diff --git a/samples/client/petstore/swift5/urlsessionLibrary/Sources/PetstoreClient/URLSessionImplementations.swift b/samples/client/petstore/swift5/urlsessionLibrary/Sources/PetstoreClient/URLSessionImplementations.swift
index 6fa4d0e20eb9b..15616ae3028d2 100644
--- a/samples/client/petstore/swift5/urlsessionLibrary/Sources/PetstoreClient/URLSessionImplementations.swift
+++ b/samples/client/petstore/swift5/urlsessionLibrary/Sources/PetstoreClient/URLSessionImplementations.swift
@@ -611,12 +611,24 @@ private class FormURLEncoding: ParameterEncoding {
         var urlRequest = urlRequest
 
         var requestBodyComponents = URLComponents()
-        requestBodyComponents.queryItems = APIHelper.mapValuesToQueryItems(parameters ?? [:])
+        let queryItems = APIHelper.mapValuesToQueryItems(parameters ?? [:])
+        
+        /// `httpBody` needs to be percent encoded
+        /// -> https://developer.mozilla.org/en-US/docs/Web/HTTP/Methods/POST
+        /// "application/x-www-form-urlencoded: [...] Non-alphanumeric characters in both keys and values are percent-encoded"
+        let percentEncodedQueryItems = queryItems?.compactMap { queryItem in
+            return URLQueryItem(
+                name: queryItem.name.addingPercentEncoding(withAllowedCharacters: .alphanumerics) ?? queryItem.name,
+                value: queryItem.value?.addingPercentEncoding(withAllowedCharacters: .alphanumerics))
+        }
+        requestBodyComponents.queryItems = percentEncodedQueryItems
 
         if urlRequest.value(forHTTPHeaderField: "Content-Type") == nil {
             urlRequest.setValue("application/x-www-form-urlencoded", forHTTPHeaderField: "Content-Type")
         }
 
+        /// We can't use `requestBodyComponents.percentEncodedQuery` since this does NOT percent encode the `+` sign
+        /// that is why we do the percent encoding manually for each key/value pair
         urlRequest.httpBody = requestBodyComponents.query?.data(using: .utf8)
 
         return urlRequest
diff --git a/samples/client/petstore/swift5/validation/PetstoreClient/Classes/OpenAPIs/URLSessionImplementations.swift b/samples/client/petstore/swift5/validation/PetstoreClient/Classes/OpenAPIs/URLSessionImplementations.swift
index 6fa4d0e20eb9b..15616ae3028d2 100644
--- a/samples/client/petstore/swift5/validation/PetstoreClient/Classes/OpenAPIs/URLSessionImplementations.swift
+++ b/samples/client/petstore/swift5/validation/PetstoreClient/Classes/OpenAPIs/URLSessionImplementations.swift
@@ -611,12 +611,24 @@ private class FormURLEncoding: ParameterEncoding {
         var urlRequest = urlRequest
 
         var requestBodyComponents = URLComponents()
-        requestBodyComponents.queryItems = APIHelper.mapValuesToQueryItems(parameters ?? [:])
+        let queryItems = APIHelper.mapValuesToQueryItems(parameters ?? [:])
+        
+        /// `httpBody` needs to be percent encoded
+        /// -> https://developer.mozilla.org/en-US/docs/Web/HTTP/Methods/POST
+        /// "application/x-www-form-urlencoded: [...] Non-alphanumeric characters in both keys and values are percent-encoded"
+        let percentEncodedQueryItems = queryItems?.compactMap { queryItem in
+            return URLQueryItem(
+                name: queryItem.name.addingPercentEncoding(withAllowedCharacters: .alphanumerics) ?? queryItem.name,
+                value: queryItem.value?.addingPercentEncoding(withAllowedCharacters: .alphanumerics))
+        }
+        requestBodyComponents.queryItems = percentEncodedQueryItems
 
         if urlRequest.value(forHTTPHeaderField: "Content-Type") == nil {
             urlRequest.setValue("application/x-www-form-urlencoded", forHTTPHeaderField: "Content-Type")
         }
 
+        /// We can't use `requestBodyComponents.percentEncodedQuery` since this does NOT percent encode the `+` sign
+        /// that is why we do the percent encoding manually for each key/value pair
         urlRequest.httpBody = requestBodyComponents.query?.data(using: .utf8)
 
         return urlRequest