A one-time license is intended for use with older versions (2019 and earlier) of QuickBooks Desktop (QBDT) that's valid for three years, reclassify. I'll provide further information on this and company file compatibility when transitioning to a different product, version, or edition of the desktop platform.

You'll utilize your QBDT license number for product activation or registration. Make sure to install the same version of QBDT as your backup company file to open it, as upgraded files cannot be used in older versions. 

You can learn more about the details above by checking out this article: Company file compatibility with QuickBooks Desktop when upgrading.

Additionally, we'd encourage you to keep QuickBooks updated so you have the latest features and product improvements. To guide you through the process, please see this article: Update QuickBooks Desktop to the latest release.

Please don't hesitate to come back to this post if you have follow-up questions about the one-time license in QBDT. I'm always here to help.