Cause
The requested audience is not covered: channel without allow_channel_audience and a granted channel, tenant without allow_tenant_audience, or a selector that was not granted or does not exist (answered the same way to avoid confirming it).
What to do
Query GET /communications/audiences and use only its references and modes.
application/problem+json
{
"type": "https://masnet.com/developers/errors/audience_not_granted",
"title": "Audience not granted",
"status": 403,
"detail": "...",
"code": "audience_not_granted",
"correlation_id": "..."
}