DNS setting for subdomain

Dear Gliders,
a new great app, created thanks to Glide, wants to find its way to your users. For this I am trying to create a custom domain for a subdomain. The Glide App should be available via app.abik.vision. However, when changing the DNS setting of the subdomain, I get an error message with the TXT entry (the CNAME entry seems to work) at a German domain provider Strato, which is not taken over because of special characters. Unfortunately the error message at Strato is very vague and I can’t reach anyone there. Do you have any idea what I could do?

Thanks a lot!