App doesn’t work

Hi,

I just bought and downloaded the email template customizer for Woocommerce.
But it seems like I can’t edit anything in the templates, because it only shows a white screen on the edit page.
I have tried looking at the app settings, but here the same problem occurs. Only white page showing.

How can you help me?

I have some screenshots of the things I describe, if you want to have a look?