Valid m.room.tombstone state event results in "Content has no replacement_room key" error

[th0mcat]

Description

When trying to send an m.room.tombstone custom state event through either devtools or Swagger, I only receive an Content has no replacement_room key error despite the replacement_room being populated in the content.

devtools

{
  "content": {
    "replacement_room": "!dwCfBTJakfZKJONWKw:matrix.org",
    "body": "This room has been replaced"
  },
  "room_id": "!GGpVnIHTefZpWGatgK:hackingfor.eu",
  "sender": "@thomcat:thomcat.rocks"
}

Swagger

{
  "content": {
    "body": "This room has been replaced",
    "replacement_room": "!dwCfBTJakfZKJONWKw:matrix.org"
  },
  "room_id": "!GGpVnIHTefZpWGatgK:hackingfor.eu",
  "sender": "@thomcat:thomcat.rocks",
  "state_key": "",
  "type": "m.room.tombstone"
}

Steps to reproduce

• devtools -> Explore room state -> Send custom state event
• https://playground.matrix.org/#put-/_matrix/client/v3/rooms/-roomId-/state/-eventType-/-stateKey- -> Paste JSON into "Example" -> Click "Try" button

Homeserver

thomcat.rocks

Synapse Version

1.121.1

Installation Method

Docker (matrixdotorg/synapse)

Database

Single Postgres, never ported from SQLite, never restored previously

Workers

Single process

Platform

Ubuntu 22.04, running synapse in docker container

Configuration

No response

Relevant log output

synapse.http.server - 130 - INFO - PUT-173 - <XForwardedForRequest at 0x76a59bb47380 method='PUT' uri='/_matrix/client/v3/rooms/!GGpVnIHTefZpWGatgK%3Ahackingfor.eu/state/m.room.tombstone/' clientproto='HTTP/1.0' site='8008'> SynapseError: 400 - Content has no replacement_room key

Anything else that would be useful to know?

No response