I believe they removed it. I read a post
here that states Google removed the pay feature (peer-to-peer transactions) from Assistant, Gmail, and Contacts. They claim that it's been returned to Contacts, but I haven't seen that. Although, they were referring to the UK in the post.
Anyway, yeah, I noticed it was missing from Gmail as well. That's not good because I liked using it there. I'm guessing there was a good reason for doing this. Most likely for security or for some legal reason. I don't really know. I did read this post from Google on their support page though:
https://support.google.com/pay/answer/9868649?hl=en
Straight from Google's mouth. They say that you can't send, request, or receive money anymore via Google Pay through Gmail, Android Messages and iMessages, Contact, or Assistant. This has been in effect since July of 2020, so it's been a little while now. You can still use all of this functionality through their
Google Pay web page or through their mobile app (GPay).
Now, the big question is how long this will last. Google has somewhat of a track record of making features and tools disappear in the night. Will Google Pay disappear?