These instructions are for ImageFramer that you download from our web site, from https://imageframer.net/download.
Mac App Store version of ImageFramer doesn't have a license key, as no Mac App Store apps use license keys, instead, your purchases are connected to your Apple ID. There's an Unlock menu in ImageFramer in the Mac App Store and there's a Restore Purchases button in the Unlock dialog that can restore your prior purchases if you ever bought them with the same Apple ID.
Steps to register ImageFramer:
Launch ImageFramer that you've downloaded from our website. You should see a watermark over the image, as you didn't input the license key yet.
The "Thank you for your purchase" email that you've received from us should include a license key and a special link that can make this registration process much easier. If you haven't received your email, you can resend your Apparent Software licenses to your email at https://www.apparentsoft.com/lost_license
This special link starts with imageframer3:// . If you can click it from your mail client, do it. If not, copy that whole link and paste it into Safari's address bar and hit enter.
This may prompt you about opening the link in ImageFramer. Agree. Then ImageFramer itself should show its licensing dialog filled in. Just follow the prompts (Validate License) and then agree to download the frame library from our server.
If, for any reason, you cannot make the link work, then copy the license key from the email. In ImageFramer, there's ImageFramer menu on the left side of the menu bar. Open it, should have an item titled "Licensing…". See the screenshot below. Select that item and Licensing dialog will come down. Paste your license key there and enter your email address (you can copy it from the email as well). Hit Validate License, you should get a "Thank You" and continue with the prompts.