How can I tell Symfony where to search for a template php file for a view?

Question

I am coding a simple Plugin for Mautic Mautic uses Symfony and hence my plugin has the directory structure (slightly different than standard symfony), which is here described Mautic Dev Docu

In my Controller I return delegateView Further Description. For this the 'contentTemplate' => 'MyPluginBundle:details.html.php', is necessary. For testing, I upload this raw plugin to the Mautic Plugin folder, and actually everythin seems to work. Firsty, some buttons are added to the dashboard.

Unfortunately, if I call the Controller the logs tell me that he is "Unable to find template "MyPlugin:details.html.php" (looked into: .../vendor/knplabs/knp-menu/src/Knp/Menu/Resources/views, [some more paths follow] I have placed my details.html.php in nearly all folders of my plugin, just be sure, he can find it. But as I get the message right, he is just looking for the file in a completly wrong directory. Therefore, my question is, how can I tell him to look in the correct folder for this file?

Thank you in advance

I have compared my code to other Mautic Controller code Form Mautic Core Bundle

From Some Plugin

I changed MyPlugin:details.html.php to @MyPlugin:details.html.php to MauticPlugin/MyPlugin:details.html.php and even to the entire path, but all without success