Teambooking Cancelation Page not working

Hi,
I’m using Teambooking plugin with enfold. There is the possibility to cancel a booked date i.e. with this link:
http://www.energo-informative-medizin.ch/wp-admin/admin-ajax.php?action=teambooking_rest_api&operation=cancel&id=42&checksum=7qJY7sYM6vmGxqpzW52FveeyuTWugNDT&show_confirm=1

But the page appears is not coming with a normal layout. It appears with no css styles.

I just had also contact with the developer. He told me:

“It should look just as a normal theme page. The styles are applied by the theme, not by the plugin.”

Is there anything to be updated by enfold in the theme or should the plugin use a different link for cancelation?
Or can I do anything to solve the topic?

Thanks a very lot for your support