In an on Premise deployment you have to make the p/ available via the pattern in URL Rewrite in IIS. My specific pattern looks like this: ^(file|link/|xas/|p/|ws/|ws-doc/|sso/)(.*) As you can see the p/ is in the pattern.
There is a setting for this on the cloud platform.
First navigate to your application on the cloud platform then go to you environment details.
Then look under the network tab and you will find a the path based access restrictions table. There is a line item for /p/ path and you have me make sure that is set to allow access.
Hope this helps!