core-lightning/doc/schemas/sendcustommsg.request.json

{
  "$schema": "http://json-schema.org/draft-07/schema#",
  "type": "object",
  "required": [
    "node_id",
    "msg"
  ],
  "added": "v0.10.1",
  "additionalProperties": false,
  "properties": {
    "node_id": {
      "type": "pubkey",
      "description": "the node specified by `node_id` must be a peer, i.e., it must have a direct connection with the node receiving the RPC call, and the connection must be established. For a method to send arbitrary messages over multiple hops, including hops that do not understand the custom message, see the `createonion` and `sendonion` RPC methods. Messages can only be injected if the connection is handled by `openingd` or `channeld`. Messages cannot be injected when the peer is handled by `onchaind` or `closingd` since these do not have a connection, or are synchronous daemons that do not  handle spontaneous messages"
    },
    "msg": {
      "type": "hex",
      "description": "must be a hex encoded well-formed message, including the 2-byte type prefix, but excluding the length prefix which will be added by the RPC method. The message types may not be one of the internally handled types, since that may cause issues with the internal state tracking of Core Lightning. We do (as of *v23.11*) allow sending of even types, but note that peers (as per the spec) will disconnect on receiving unknown even types"
    }
  }
}