CMS running on web page but Windows Displays cannot be added

Hi, we are running a 1.7.9 on the web, we noticed the only Display stopped getting updates, after troubleshooting, we decided to remove the client ensure that the hardware ID was also changed and tried to save the settings
we kept receiving the underlying connection was closed the connection was closed unexpectedly
we gave up on as windows 7 machine and tried another machine Win 10 installed the old 1.7.9 and separately 1.8.10 client (fresh Installs) and we get the same error,.

on the CMS display we dont see any error logs…
We are unable to pin point what might be issue
cms rnning on https://www.sdimktg.ca/xibo
at the moment, the CMS shows only another old display, but we are unable to see what the problem might be… all computers are behind the same firewall and no changes have been made to it… we tried on a separate network… same issue…
any help would be appreciated

Can you confirm whether you are using Android or Windows for the player? If you are using a Windows player, it is possible that the issue is due to your CMS being an older version than the player. Windows players are not backwards compatible and so you may need to upgrade the CMS to the latest version to resolve the issue.