Unable to activate licence (pmdg777msfs)

I have just purchased a single CDU licence for the MSFS version of the PMDG 777.

It was purchased from Simmarket.

 

 

On trying to activate the licence I enter the serial number and select the 777 CDU then hit send. This then comes up with the following error message:

“The underlying connection was closed; An unexpected error occurred on a send”

 

This same error message came up when I tried the “get help” option .

I have tried several times and have also reinstalled the program with no joy.

I already have a valid license for the PMDG 737.

 

I have tried disabling the firewall and I don’t run any av software as you suggested by email.

Any other ideas so I can use the software I’ve paid for or has anyone else had this issue and how was it resolved.

 

Steve