Would like to know how to trouble shoot that portal proxy 403 error?
In the network traffic when I load the web map, I saw two web request, one is with proxy (got 403), one is with direct request (got http 200).
When I browse the https://xxx../MapServer?f=json, it is happily browse also.
But when it is trying to browse through portal proxy, it always, 403 error.
It is happening in portal for arcgis 10.5.1.
Than Htet Aung