Calendar for bolt: TWIG templates not recognized

[tskraft]

Hello, I want to add a calendar to my bolt website. This makes use of Twig templates for Doctrine database CRUD and for the page that renders the calendar. I tried putting the controller in the /src directory and the TWIG templates in the default Symfony /templates directory. I get error "Unable to find template"
How can I fix that? Thank you very much!