This is a read-write integer specifying the payload size, in bytes, that the coder should produce when generating fax data for this peer, with 0 meaning the coder's default fax payload size should be used instead. An admin adjusts this the same way as the voice coder-bytes setting, but specifically for the fax-relay payload produced by this peer's configured coder. For example, leaving this at 0 lets the gateway automatically apply whatever default fax payload size is appropriate for the coder configured on the peer.