After selecting Extensions > Khan2GC > Setup > Launch Setup, click on the second section, License.
In order to use Khan2GC, you will need to register for a license. All add-ons come with a 14-day free trial, no credit card required. To continue using the add-on after the 14 days, you will need to provide payment information to purchase a yearly license. After signing up for your 14-day free trial, or purchasing a yearly license, you will receive an email from BunzApps with your License ID in it.
Copy and paste the License ID into the License ID field in the setup sidebar. Then click Save. Wait until the status bar the bottom of the setup sidebar says Settings Saved before proceeding to the next section.
If there is an issue with your License ID, a notification box will appear explaining the issue.
Note that you can only use your License ID in a spreadsheet in the Google account associated with the email you provided while signing up for a free trial. If you need to change the email associated with your License ID, or have forgotten/lost your License ID, please contact me.