With the latest LongoMatch version there is not need to manually insert your license key in order to activate your upgraded plan, so please, make sure you have the LongoMatch version 1.8.4 available in his link here or clicking on "LongoMatch" from the top bar menu and select "Check for updates".
Once is downloaded and installed, you will have to log in using your usual credentials and after the Log in page, a dropdown menu will appear and you will be asked which one of your available licenses you want to activate.
Additionally, if you need to do this process manually, please check this link here to see how to change your license.