I have downloaded the free version of DaVinci Resolve, but it requires my license key.

Blackmagic DaVinci Resolve Studio is the full version of DaVinci Resolve, while DaVinci Resolve is the free version. These are two separate software packages available on the Blackmagic Design website. Please ensure that you have the proper version.

If you are prompted for an Activation Key upon launching the application, the Studio edition of DaVinci Resolve is installed on your computer. If you are attempting to utilize the Studio edition of DaVinci Resolve, you must either enter your activation key when prompted or connect the USB dongle and restart the software.