Did you resolve this issue?

It looks like a javascript error on the config page - there was an issue with a bad German translation at one point that caused this but but this was fixed a long time ago. Make sure your language files are all up to date

Thanks, Geraint.

The issue is not resolved, but I tweaked it: seems like the target page has to be a JEvents menu point. So what I've done is, I attached the subscription module to the event detail page. Works so far.
The issue with the blank config page is not resolved. The german translation is the latest (as every part of the site is); but for configuring, I have to switch the backend language to english. Then back again to german, when finished. This way, it works

Thanks anyway!
Martin

Sorry - I've been in bed for a week with Covid. First time I've had it (after the vaccinations wore off) and I have been completely out of action

If you enable Joomla debug mode and maximum error reporting you may get more information about the blank config page which we can then look to resolve

Dear Geraint,

I wish you a soon recovery! I had it last year, inspite of three vacs and I can feel with you.

We leave it as it is: For configuring, I switch to english backend language and then back to german again.

Best regards
Martin