Cause
schedule requires the campaign to have starts_at and ends_at.
What to do
Save the campaign with both dates before scheduling it.
application/problem+json
{
"type": "https://masnet.com/developers/errors/dates_required",
"title": "Dates required",
"status": 422,
"detail": "...",
"code": "dates_required",
"correlation_id": "..."
}