Microsoft Remote Desktop for Mac won't connect from an external network (but will from Windows)

Hopefully I am explaining this properly.

I can successfully Remote desktop connect if I am on my local wifi network at work, but when I go home and try to connect from a different network it fails.

I can connect easily with my PC from home , but not Mac High Sierra or Ipad for that matter.

I opened up the port for RDC in my ATT router and I use that IP address:port. This works with PC to PC.

I have the latest version of MRD, I even tried the beta but that had the same version # and failed as well.

I get error code 0x0300008 or 0x300005. Mainly saying the certificate failed.

The host PC is running win7 pro 64.

My PC at home is a small screen laptop, I would really prefer to use my MBPR since it is a much larger screen.

And yes team viewer works, but I'd like to solve this since I've spent so much time.

Thanks for your help,

Steve