[5.3] Messages api issue - the webservices API for creating and patching messages is not working

administrator/components/com_messages/forms/message.xml

@@ -1,6 +1,13 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <form addfieldprefix="Joomla\Component\Messages\Administrator\Field">
 	<fieldset>
+		<field
+			name="message_id"
+			type="hidden"
+			default="0"
+			filter="int"
+			readonly="true"
+		/>
 		<field
 			name="user_id_to"
 			type="UserMessages"

administrator/components/com_messages/src/Model/MessageModel.php

@@ -349,6 +349,7 @@ public function save($data)
 
         if (isset($table->$key)) {
             $this->setState($this->getName() . '.id', $table->$key);
+            $this->__state_set = true;
         }
 
         if ($config->get('mail_on_new', true)) {