Problem with the federation. "SynapseError: 403 - You are not invited to this room"

[arpsyapathy]

Hello!

There was a problem with the federation.
Most likely, there was a desynchronization of data in the synapse database.
When I add a user to a group on one RC server, I see error "SynapseError: 403 - You are not invited to this room" in the logs on the second RC server.
In RC, user gets into the room, but in Synapse it hangs in the invite state and must accept it manually.
The user can write messages in RC, but no one will see him on another RC server, since in the matrix he hangs in the invitation state. If you accept the invitation manually through the matrix API, everything starts working. At the same time, direct messages in federation works fine. The problem is only with groups/rooms.

Has anyone encountered such a problem? How did you solve the problem?
Thanks you in advanced

[MostlyKIGuess]

This issue arises from desynchronization between Rocket.Chat and Synapse in a federated setup, particularly affecting group membership.

Did you make sure that both Synapse servers use compatible Matrix protocol version ? and that homeserver.yaml federation settings are correctly configured.
Check Synapse logs on the second server to identify why the user remains in the "invited" state. Or just send them here.

Easy fix-
Use the Matrix API to manually accept the invitation as a temporary fix.

[arpsyapathy]

@MostlyKIGuess

Everything was set up strictly according to the documentation of the RC.
Everything worked fine until a certain point.
Now dm works fine, the problem is only in groups.
I will check the logs later and write what I find there.

[arpsyapathy]

@MostlyKIGuess
In logs i see only "POST-22 - Denying new event <FrozenEventV3 event_id=" with "SynapseError: 403 - You are not invited to this room"and nothing else that could refer to the problem.

But I roughly tracked some cases when it works and when a problem occurs:

1. If an user on server1 adds a new user from server2 to an old room on server1 - PROBLEM
2. If an user on server1 adds an old user from server2 to an old room on server1 - OK
3. If an user on server1 adds a new user from server2 to a new room on server1 (created after the new user appeared) - OK
4. If an user on server1 adds a old user from server2 to a new room on server1 - PROBLEM

[reetp]

Please fill out a bug template properly as per this (use the template, fill it in and and paste here - don't create new issue)

https://github.com/RocketChat/Rocket.Chat/issues/new?assignees=&labels=&projects=&template=bug_report.md

Note this as well.

https://gist.github.com/reetp/a66149d5f060f260643a353ca7067a98#information-that-support-or-devs-will-require