Returned when you have API access but your plan’s granted scopes don’t include the one this endpoint declares. The missing scope is in the scope field. 
{ "error": { "code": "scope_not_granted", "message": "scope 'vessels:fleet:read' is not granted to this partner", "scope": "vessels:fleet:read" } }
Fix — each capability page lists what it needs (the Requires note). If a capability you expect isn’t enabled for your account, talk to CrewPass. See how access works.