I’ve the same problem on my mta-sts-karolak-fr page, i cannot verify the custom domain mta-sts.karolak.fr.
The DNS seems correctly configured:
> host mta-sts.karolak.fr 126.96.36.199
Using domain server:
mta-sts.karolak.fr is an alias for mta-sts-karolak-fr.pages.dev.
mta-sts-karolak-fr.pages.dev has address 188.8.131.52
mta-sts-karolak-fr.pages.dev has address 184.108.40.206
mta-sts-karolak-fr.pages.dev has IPv6 address 2606:4700:310c::ac42:2ed1
mta-sts-karolak-fr.pages.dev has IPv6 address 2606:4700:310c::ac42:2d2f
What i also does not understand is that it was working previously, it seems to have “unconfigured” itself recently.
I tried to remove the custom domain and re-add it, does not help.
My wonderful colleague @dmartin1 saw the issue. You have added mts-sts.karolak.fr to Pages and I can confirm I can see it internally. However, your records are setup for mta-sts.karolak.fr (note the third character changed from s to a).
Checking mts-sts.karolak.fr there are indeed no DNS records: