Get Request for Website status Code :200 works with collection, but it does not work with monitor for the same collection and it gives 403. I even do not use any token,authorization or header parameter for the collection.
I think it’s due to client certificates not being supported on the Postman Monitoring yet. I had the same issue. You probably have some client-side certificates configured locally on your postman, but those are not taken into account when you use the Postman Monitor.