Hey Alberto,
I'd suggest posting a thread like this on StackOverflow, as it's more likely to be seen and acted on in that context. This forum is more for general discussion of issues.
With that said, I'll advise you to triple-check that you've followed all the steps in
the docs for setting up a Custom Domain, and also identity the following information when you make your question:
- The domain you're trying to use, so other users can run nslookup or similar commands
- The steps you've followed so far
I wish you the best of luck!