Use this guide to troubleshoot the problems with activating Snagit on a Proxy Server.
Before proceeding, please make sure that the computer that Snagit is being installed on meets the minimum system requirements. Also make sure that all Windows updates are installed. See this Microsoft support article for instructions on how to check for updates.
Add the following addresses in your proxy server to the Allow List
Snagit also needs to be able to communicate over ports 443 and 80.
*You may only need port 443.