Cause
The source_revision is lower than the last accepted one in Communications. details.current_source_revision reports the current one.
What to do
Discard the stale submission or resend with a revision higher than the current one.
application/problem+json
{
"type": "https://masnet.com/developers/errors/stale_source_revision",
"title": "Stale source revision",
"status": 409,
"detail": "...",
"code": "stale_source_revision",
"correlation_id": "..."
}