Publishing agent on seperate domain

Hi,
I am migrating from an on premises citrix xenapp environment to a Mac OSX desktop environment.
I’ve setup a single server Paralles RAS on Azure to stream 3 or 4 windows applications to the Mac with RAS. Server is licenses and running well with the couple applications i’ve published so far.

I was hoping i could convert one of my old on Prem VM’s to a temporary (3-4 Months) publishing agent to host a couple of the more complicated apps whilst i am migrating users off citrix to macs and give me time to migrate those apps to the azure server.
We have a point to point VPN setup between azure server and our premises, but i wasn’t able to add the on prem server as a publishing agent to the RAS farm on azure. It will only let me add servers on the azure domain. Is there any thing in particular i need to do? Would this type of setup work? Or should i just load a whole new farm on premises for now and have the clients log into 2 farms. Assuming licensing allows that ?

Any help would be appreciated.