Cause
The campaign is already closed, cancelled or archived.
What to do
It does not accept that action. Create another campaign with another external_id.
application/problem+json
{
"type": "https://masnet.com/developers/errors/campaign_closed",
"title": "Closed campaign",
"status": 409,
"detail": "...",
"code": "campaign_closed",
"correlation_id": "..."
}