Hello, Marko. I'm Greg, here to help you with this.
You will need to contact Microsoft Support to move the license to the new hardware. Contact Microsoft Support at https://support.microsoft.com/en-us/home/contac...
Explain the problem to the Virtual Assistant and keep asking for an agent, to get chat or a call back on week days.
If the retail key you bought had converted to a Digital License then you might also be able to move it by signing in with the same Admin account and running the Activation troubleshooter to see if it offers to move the license to the new hardware, as shown here:
https://support.microsoft.com/en-us/windows/rea...
If Support tells you it is not a genuine key then be aware that discount keys are almost always bogus, there are no deep discounts for Windows software. You can contact the seller to see if they will make it good. You can also report the seller to Microsoft for piracy: https://www.microsoft.com/en-us/howtotell/cfr/r.... Sometimes if you let the seller know you are doing this they will make it right rather than undergo an investigation for piracy.
Also do you have any old Windows 7, 8, 8.1, 10 or 11 retail licenses you are not using? These might be able to be used to get free Upgrade, even for a Clean Install.
I know you are trying to do the right thing and hope this helps. Feel free to ask back any questions. Based on the results you post back, I will have other suggestions if necessary.
____________________________________________
Standard Disclaimer: There are links to non-Microsoft websites. The pages appear to be providing accurate, safe information. Watch out for ads on the sites that may advertise products frequently classified as a PUP (Potentially Unwanted Products). Thoroughly research any product advertised on the sites before you decide to download and install it.