RDWeb External Access Failing

I just installed a Server 2012 R2 RDS deployment.  I have published Apps and they are all working internally.  Externally they are failing.  I have installed ad configured the RD Gateway, as well as a 3rd party SSL certificate.

I am assuming I have a firewall issue.  I have opened port 443 ONLY so far.  Do I need more ports open to allow remote Apps externally?
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Cliff GaliherCommented:
Not with RDGateway. 443 is all you need from external to the RDGateway server.
BSModlinAuthor Commented:
So what do you think I am missing??
Cliff GaliherCommented:
URL or SSL issues most likely. With no errors, it is tough to be more specific.
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BSModlinAuthor Commented:
My internal FQDN is server1.ABC.local and my external name is apps.ABC.com.  My SSL cert matches the external name.  Is that a supported configuration?
Cliff GaliherCommented:
As long as you configured RDGateway that way via server manager.
BSModlinAuthor Commented:
Can you provide a link so I can verify that? Not sure where to check.

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BSModlinAuthor Commented:
Ok... I have managed to change the URL to the external FQDN with a powershell script I found online.

Now I believe I have a permissions issue....  When I access the Remote App site internally it works, but once logged into the web page... and I launch an app it prompts me for credentials again.. but then the app launches....

When I go to do the same thing externally, the same thing happens but when I put the credentials in to launch the app it fails and gives the attached error message....

What could this be?
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Windows Server 2012

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