Room join fails with 404 `M_NOT_FOUND` `Not found in database`

[lilioid]

Describe the bug

When using the bot sdk to join a very large and very federated room, the call to POST /_matrix/client/v3/join/… fails with my homeserver returning { errcode: 'M_NOT_FOUND', error: 'Not found in database' } and status 404.
I believe this might be an error in MatrixClient.ts:1144 which sets the server_name GET parameter even though the Matrix Client-Server API Spec only describes the via GET parameter.

To Reproduce

1. Try to join a room with a large number of federations and a large number of via servers (around 593 in my case)
2. See error

Expected behavior
The bot should be able to join the room.

Log snippet

{@<redacted>:<redacted>} Processed request: 1.254sec/0.000sec ru=(0.018sec, 0.001sec) db=(0.005sec/0.013sec/9) 57B 404 "POST /_matrix/client/v3/join/!<redacted>?server_name=<redacted>&server_name=<redacted>&server_name=<redacted>…

Additional context
I am using Synapse as my Homeserver and am doing a client.lookupRoomAlias() before joining. The via servers are discovered as a result of this lookup and copied over to client.joinRoom().

I can see how it is an issue in itself that the room has almost 600 via servers but believe that the server_name GET parameter is incorrect regardless.