After you have activated ExtendSim, the Activation Dialog should not appear again spontaneously. If it does appear, it could indicate that:

The license file (extendsim.lic) has been moved, deleted, renamed, modified, or replaced by someone else's license file:

The license file should be located in the ExtendSim folder that contains the user-modifiable files (libraries and example models); by default, that folder is UserName/Documents/ExtendSim10.

There should only be one .lic file in that ExtendSim10 folder and it must be named extendsim.lic.

Each license file is signed as being specific to the Activation Key that was used and the device that ExtendSim was activated on. Do not modify the license file or attempt to use someone else's license file.

There is more than one installation of the same ExtendSim product on your device.

Someone else may have installed the same ExtendSim product on this device. For example, maybe an Admin installed an Individual license of ExtendSim to their account and you installed the same license to your account. In this case, the Documents folders for those accounts will each have an ExtendSim10 folder. The solution is to uninstall ExtendSim from all duplicate locations. (If you want multiple users on one device, you must purchase a Node-Locked license.)

You may have improperly installed a Trial version when updating ExtendSim. To update existing files, the Trial version must be installed using the exact same folder name and to the same location as the current installation. If that didn't happen, there will be two installations of the same ExtendSim10 product, as indicated in your Documents folder. The solution is to uninstall the Trial version and reinstall it over the existing installation so that it updates the ExtendSim 10 files.