diff --git a/core/config/schema/core.data_types.schema.yml b/core/config/schema/core.data_types.schema.yml
index 25008f46e8..01a1eeee95 100644
--- a/core/config/schema/core.data_types.schema.yml
+++ b/core/config/schema/core.data_types.schema.yml
@@ -280,7 +280,7 @@ config_entity:
       constraints:
         Length:
           max: 128
-          maxMessage: 'UUID may not be longer than 128 characters.'
+          maxMessage: 'UUID: may not be longer than 128 characters.'
     langcode:
       type: string
       label: 'Language code'
diff --git a/core/modules/rest/tests/src/Functional/EntityResource/ConfigTest/ConfigTestResourceTestBase.php b/core/modules/rest/tests/src/Functional/EntityResource/ConfigTest/ConfigTestResourceTestBase.php
index 8d62290d62..b89a2718dc 100644
--- a/core/modules/rest/tests/src/Functional/EntityResource/ConfigTest/ConfigTestResourceTestBase.php
+++ b/core/modules/rest/tests/src/Functional/EntityResource/ConfigTest/ConfigTestResourceTestBase.php
@@ -32,6 +32,11 @@
   /**
    * {@inheritdoc}
    */
+  protected static $firstCreatedEntityId = 'llama';
+
+  /**
+   * {@inheritdoc}
+   */
   protected function setUpAuthorization($method) {
     switch ($method) {
       case 'GET':
diff --git a/core/modules/rest/tests/src/Functional/EntityResource/EntityResourceTestBase.php b/core/modules/rest/tests/src/Functional/EntityResource/EntityResourceTestBase.php
index 5c2a99f63f..42c42e5bb5 100644
--- a/core/modules/rest/tests/src/Functional/EntityResource/EntityResourceTestBase.php
+++ b/core/modules/rest/tests/src/Functional/EntityResource/EntityResourceTestBase.php
@@ -693,10 +693,15 @@ public function testPost() {
 
     // DX: 422 when invalid entity: multiple values sent for single-value field.
     $response = $this->request('POST', $url, $request_options);
-    $label_field = $this->entity->getEntityType() ->hasKey('label') ? $this->entity->getEntityType() ->getKey('label') : static::$labelFieldName;
-    $label_field_capitalized = $this->entity->getFieldDefinition($label_field) ->getLabel();
-    $this->assertResourceErrorResponse(422, "Unprocessable Entity: validation failed.\n$label_field: $label_field_capitalized: this field cannot hold more than 1 values.\n", $response);
 
+    if ($this->entity instanceof ConfigEntityInterface) {
+      $this->assertResourceErrorResponse(422, "Unprocessable Entity: validation failed.\nlabel: This value should be of the correct primitive type.\n", $response);
+    }
+    else {
+      $label_field = $this->entity->getEntityType()->hasKey('label') ? $this->entity->getEntityType()->getKey('label') : static::$labelFieldName;
+      $label_field_capitalized = $this->entity instanceof FieldableEntityInterface ? $this->entity->getFieldDefinition($label_field)->getLabel() : 'label';
+      $this->assertResourceErrorResponse(422, "Unprocessable Entity: validation failed.\n$label_field: $label_field_capitalized: this field cannot hold more than 1 values.\n", $response);
+    }
 
     $request_options[RequestOptions::BODY] = $parseable_invalid_request_body_2;