Does a website have to be listed in Watchtower for a passkey to work on that site?

I logged on to a website that I use sometimes, and it said I could create a passkey. So, I created it and saved it in 1Password. The next time I logged in, it did not recognize the passkey. So, I checked Watchtower, and did not show the particular website in question.. I thought it was rather curious because the website is one that millions of people use. Anyway, is that simply the way it works? I.e., if Watchtower doesn't list it, then it won't work?