Cause
A highlight without a target requires can_create_standalone_highlights and the highlights.content path.
What to do
Provide a target or ask the administrator to grant standalone highlights.
application/problem+json
{
"type": "https://masnet.com/developers/errors/standalone_not_granted",
"title": "Standalone highlight not granted",
"status": 403,
"detail": "...",
"code": "standalone_not_granted",
"correlation_id": "..."
}