Cause
The event already has a delivery in progress at this destination.
What to do
Retry later.
application/problem+json
{
"type": "https://masnet.com/developers/errors/delivery_in_progress",
"title": "Delivery in progress",
"status": 409,
"detail": "...",
"code": "delivery_in_progress",
"correlation_id": "..."
}