Fixed #14350

CHANGELOG.md

@@ -8,6 +8,7 @@
 - `craft\behaviors\SessionBehavior::setSuccess()` and `getSuccess()` use the `success` flash key now, rather than `notice`. ([#14345](https://github.com/craftcms/cms/pull/14345))
 - Exception response data no longer includes an `error` key with the exception message. `message` should be used instead. ([#14346](https://github.com/craftcms/cms/pull/14346))
 - Fixed a bug where read/write splitting was always getting disabled for GraphQL POST requests. ([#14324](https://github.com/craftcms/cms/issues/14324))
+- Fixed an error that occurred when adding a new block to a Matrix field with an overridden handle. ([#14350](https://github.com/craftcms/cms/issues/14350))
 
 ## 5.0.0-beta.1 - 2024-02-08
 

src/controllers/MatrixController.php

@@ -79,7 +79,13 @@ public function actionCreateEntry(): Response
         $siteId = $this->request->getRequiredBodyParam('siteId');
         $namespace = $this->request->getRequiredBodyParam('namespace');
 
-        $field = Craft::$app->getFields()->getFieldById($fieldId);
+        $elementsService = Craft::$app->getElements();
+        $owner = $elementsService->getElementById($ownerId, $ownerElementType, $siteId);
+        if (!$owner) {
+            throw new BadRequestHttpException("Invalid owner ID, element type, or site ID.");
+        }
+
+        $field = $owner->getFieldLayout()?->getFieldById($fieldId);
         if (!$field instanceof Matrix) {
             throw new BadRequestHttpException("Invalid Matrix field ID: $fieldId");
         }
@@ -94,12 +100,6 @@ public function actionCreateEntry(): Response
             throw new BadRequestHttpException("Invalid site ID: $siteId");
         }
 
-        $elementsService = Craft::$app->getElements();
-        $owner = $elementsService->getElementById($ownerId, $ownerElementType, $siteId);
-        if (!$owner) {
-            throw new BadRequestHttpException("Invalid owner ID, element type, or site ID.");
-        }
-
         /** @var Entry $entry */
         $entry = Craft::createObject([
             'class' => Entry::class,