There is no functional difference between the free and paid version. The free version shows a dialog prompting you to upgrade at a random interval. You can buy a license to remove the dialog.
You can use the free version forever.
Click the upgrade link at the bottom of the purchase page then enter your old license key to upgrade.
If you purchased Prepros in the last 6 months you can upgrade for free. You have to pay $19 otherwise. You can continue using Prepros 6 if you don't want to upgrade.
Please use the following links to download Prepros 6.
You can use your license on as many devices as you want as long as you are the only primary user of those devices.
Enter your email address here to receive an email with your license key.
First make sure you have not enabled "Do Not Disturb" mode, then go to Settings app then enable notifications.
Please delete one of the following configuration folders depending on your OS. That will reset all Prepros settings.
Please email firstname.lastname@example.org with your question.