Hopefully this will self-resolve now — finally figured this out! Newbie saying 'hi' here. 👋
If you're curious, I first got stuck on registering the TXT entry for forum.pianotell.com because the latter is configured as a CNAME. TXT is not apparently not compatible with CNAME and there was no indication of any problem when I registered the TXT entry. Good number of hours/days wasted supposedly waiting for DNS propagation.
Fortunately, Google provides an alternative where you can register a CNAME for a random domain. So I registered a new CNAME for <randomstring>.pianotell.com. Google was not picking up the update and all the docs say DNS takes 72 hours to propagate, etc.
Turns out that was not the problem. I needed to register a CNAME for <randomstring>.forum.pianotell.com and not <randomstring>.pianotell.com. Grrr.
Obvious once you know it, I guess? So Google and Bing both have the site map now...