Response from /knock after /invite does not conform to the specification

[matrixbot]

This issue has been migrated from #16735.

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Description

The specification allows re-knocking after having been invited (https://spec.matrix.org/v1.9/client-server-api/#mroommember).

However, Synapse returns a different response if you re-knock after having been invited:

{'errcode': 'M_FORBIDDEN', 'error': 'You are already invited to this room'}

Steps to reproduce

• Create a room
• Invite user to a room
• Knock on the room as an invitee

Homeserver

local

Synapse Version

v1.93.0

Installation Method

Docker (matrixdotorg/synapse)

Database

SQLite

Workers

Single process

Platform

Docker Container (matrixdotorg/synapse:v1.93.0)

Configuration

We use the default homeserver options, but with ratelimiting disabled.

Relevant log output

n/a

Anything else that would be useful to know?

No response