Hi Peter,
thanks for your answer.
I have made 3 printscreens and uploaded them on this page:
https://ferienwohnung-alpenrose-adelboden.ch/test-2/?lang=nl
Translation of the pop up:
An error occurred while installing your license key.
Try again. If the problem still occurs, then contact Wordfence support.
Hopefully you can help me any further?
