unsupported_join_rule· code· HTTP 422· scope bothA third-party (3PID) invite claim targeted a join-rule Realm whose continuation profile is outside v1 base conformance (e.g. knock_restricted) and the deployment has not declared the required candidate profile in ak.find.directory.read.describe.v1 / ak.account.describe. The verification service MUST reject the token claim instead of silently downgrading. See zh/sync/third-party-invites.md §4.3.