Did you try to completely log out and log back in again?
If that doesn’t help, I would deinstall and reinstall.
Which app? Good question… My hunch would be to try it with desktop app first. But it could also be that the mobile app has a “hiccup” and doesn’t succeeds in really sending the request, I guess.
@anson, one or both of your phone and computer has probably upgraded its app recently. Log out on MacOS then log in again using your master password. Perhaps do the same on the phone. Logging in with another device does not work until it is “proven” the target can log in by itself. At least, that is my reading and experience.