Here is the current state of GameMaker 8.1 licensing and what you can do: 1. Official Availability Removed from Sale: YoYo Games officially removed GameMaker 8.1 from sale on May 18, 2015 . You can no longer purchase a new Pro license. Sunset Support: Technical support for version 8.1 ended in License Activation Issues:
To ensure that your license key is genuine and valid, follow these steps: license key for game maker 81 pro link
Because the software is deprecated, the community often discusses alternative ways to keep old projects alive: Is GameMaker 8.1 Standard no longer supported? Here is the current state of GameMaker 8