If an error "License key is not valid. Please contact your administrator." appears when logging in using Check-in app, this may imply to several things:
To resolve this, please navigate to your Tickera account here and copy your license key visible in the upper right corner of the page (see the screenshot below)
Although you should always use copy/paste method when copying your license key from your Tickera account and pasting it to Tickera Settings on your website, wrongly entered license keys happened before and will inevitably happen again. So, if the your License Key field in Tickera Settings has something entered to it but you're still getting the error in Check-in app, please check if you have entered it correctly. Please note that LICENSE KEY: is not part of the actual license key and you should copy values after the colon (:) punctuation mark.
The same error will appear if your license key has expired as Check-in apps require valid license key in order to work properly. You will know if and when your license has expired if you log in to your Tickera account and get a message "For continued updates and support please purchase/renew your membership" (see the screenshot below). To renew your license, simply click Renew button which will then lead you through the license renewal process.