SynapseError: 404 - Room alias #slack_TEAMNAME_XXX:MATRIXSERVER not found

[DerBeutlin]

I could not receive any slack messages in Matrix although the messages were received by the bridge. Instead I got the following error in the terminal

SynapseError: 404 - Room alias #slack_TEAMNAME_XXX:MATRIXSERVER not found

This got "fixed" by adding

  aliases:
    - exclusive: false
      regex: '#slack_.*:MATRIXSERVER'

to the slack_registration.yaml

[twouters]

Just for reference, I've started seeing the following messages earlier this week for messages arriving from new Slack users or joining a new Slack room:

Tue, 15 Jan 2019 08:04:27 GMT matrix-puppet:slack:app This application service has not reserved this kind of alias.
[-] POST http://localhost:8008/_matrix/client/r0/createRoom (AS) HTTP 400 Error: {"errcode":"M_EXCLUSIVE","error":"This application service has not reserved this kind of alias."}

I think this change is the reason: matrix-org/synapse#4063
Synapse now checks if the AS is allowed to create a room alias while it used to perform the check on the matrix user.

[twouters]

Whoops, duplicate of #72 ?