Remote desktop client dosen't work on new iOS device

Question

Hello,

We have just bought a new iPad (iOS15.1) and when configuring RD Client (V 10.3.6 5090) to access our server (Windows Server 2008) we get error 0x204.

We are in the same local network and with the same configuration as other devices that can connect (other iPads or computers with Windows), when we are testing there is no one else connected and we have done it with the IP and the name of the device, but it doesn't work.

What could be happening? Is it the application, the server, the Firewall?

Thanks for your help!