Can't join a room with room membership access over federation

[GearKite]

Trying to join a room with access set to space members over federation results in:
MatrixError: [403] Answer from example.com: [403 / M_FORBIDDEN] M_FORBIDDEN: Event is not authorized.

Steps to reproduce:

1. Create a space
2. Create a room under that space with Visible to space members
3. Invite a user on another homeserver to the space
4. Attempt to join the room from the other homeserver

Doing this with 2 accounts on a single homeserver seems to work fine.

[Kimiblock]

Yeah this happens to me. If one add another space hosted on Synapse to the access list, others can join.

[yellows111]

Yeah this happens to me. If one add another space hosted on Synapse to the access list, others can join.

What do you mean by this? This is very vague.

What does "add another space hosted on Synapse" imply? What's a "space" in this context? A room?

Does that mean join another room from the remote server running Synapse to a user on the Conduwuit server (local)?

[Kimiblock]

No, I mean that a remote server (only tried Synapse) cannot join a room which is hosted on conduwuit and is restricted to a space on conduwuit. Upon adding a space hosted on Synapse to the allow list, other servers’ users can join. This is very weird and discovered when I host some bridges for the Arch community.

…

-- Sincerely, Kimiblock