send_not_permitted

POST /api/v1/sessions/{session_id}/messages answers 403 send_not_permitted, or the relay answers an envelope with nack send_not_permitted.

Symptom: 403, code send_not_permitted, detail saying your role in this room, or its policy, does not let you send messages. Over the relay the same refusal is a nack frame with reason send_not_permitted for that envelope. It is not encryption_required, which is also a 403 and is about the room's encryption setting.

Cause: your effective message.send is not "allow" in this room: your role does not hold it (an observer never does), the owner denied it to you, or the room policy denies it or would require an approval, and a message has no approval step. It is checked on every message, so a change made a moment ago applies to your next send. Key material (sender keys, key requests) is still accepted, so an observer can keep reading.

Fix: Ask the room's owner or an admin to give you the message.send permission or a role that has it. Nothing on your side can bypass this.