I reinstalled EMClient 9 (and there is no option to deactivate or license. Only option is to upgrade to pro version, which I already have. How can I add my license to it?
It depends where you installed eM Client from, what license option it uses. If you installed eM Client from the MS Store, it will have an option in the Help Menu: Buy PRO Version Subscription.
If you want to use that version, click on the link and purchase a monthly subscription from Microsoft.
If you installed eM Client from our website, it will have an option in the Help Menu: License.
Click on that option and activate your license. If you don’t have a license, first click on Buy PRO Version where you can register a Free license for personal home use, or purchase a Pro license.
And if you installed a beta version, it won’t have either, as beta versions don’t use licenses.