I've been using the Remote Desktop successfully for a couple of years or so, now (both on Windows & MacOS and am looking forward to a Linux version), and I haven't come across this issue before. Just installed the latest version of Remote Desktop (free version) on a Windows tower PC (version: 2.5.0.83) apparently without any issue, but when I try to add the new id to my Mac (running build: 1.2.1.8 (free version) under MacOS Catalina 10.15.7) adding the encryption key fails with the following error:

Warning
Public key must be base64 string.

I've checked the encryption key and it only consists of numbers, upper and lower case letters aside from the final two characters which are the equals signs.

The only thing I've noticed that is different from other entries added to the address book is that the new id consists of numbers and letters whereas all previous ids have been just numbers.

When I try connecting without an address book entry I get the following error:

Error
Service key request failed.

If I try to connect from another Windows PC running the same version of Remote Desktop the following seemingly equivalent error is returned when adding the encryption key and clicking on the OK button:

Invalid encryption key format

If I disable encryption I can access the PC using the pin, but that will be no good the remote unattended access over the Internet.

Is this a bug? Is there some other configuration that needs to be set?

Any thoughts on how to resolve the issue would be greatly appreciated.