Accessing to RemoteApp Externally via RDWeb

I recently started trying to deploy RDWeb to allow external access of RemoteApp.

I have configured a server that is running Remote Desktop Host and also RD Web Connection. There are no TS Gateway or RD Gateway and any other roles installed on this server. 

I can access to the page and launch the RemoteApp internally using the internal address 

https://servername/rdweb 

I perform a NAT on my firewall to allow external access

CLIENT -> INTERNET -> FIREWALL -> RDWEBSERVER

I can see the page loads

https://remote.companydomain.com/rdweb 

But when I launch the apps, I get the error

Remote Desktop can't connect to the remote computer for one of the reason

1) Remote access to the server is not enabled

2) The remote computer is turned off

3) The remote computer is not available on the network

Make sure the remote computer is turned on and connected to the network, and that remote access is enabled

Only Port 80 and 443 were allowed externally.

Thanks