Butting in, saw this as I was searching for crossposting info… the atproto-did file does not appear to be in place on your site (it should be publicly available if it’s there).
I figured this out. It’s a bug when the custom domain name doesn’t match the feed URL for your account. I updated your feed URL and now it’s working great:
https://samdavies.me/.well-known/atproto-did
You should be able to verify the file in Bluesky now.
I’ll get the root issue fixed for other users later too.