According to me, the fact that you bought it on PB does not cause the problem.
I start being out of my tricks so just the last one that I have in my sleeve:
Open the folder C:\Program Files\Scaler Music\Scaler 3.
You should see three files:
Please check their Date modified and let us know. I suppose that all should be earlier than 2025-08-28, somewhere in July. If I am right (I am pretty sure I am 
), this is standalone and its uninstaller.
Than the last trick:
Please right-click on the unins000.exe (1) and in the context menu select Run as administrator (2):
Accept the prompts, if any. Once the uninstall finishes, check that no files stay in the folder. If there is any, delete them manually.
Also delete the file that I previously suggested (Scaler 3.settings).
Maybe a reboot would be a good thing at this point. It costs nothing (and I recommend another one after the installation).
After all, install Scaler 3 v 3.1.2. (check the version number in the zip file name). Check the dates of the three files. Scaler3.exe should have Date modified of 2025-08-28 and the other two, probably the current date. Let us know if this is not the case or if the installation failed (not supposed).
Reboot your PC.
Start standalone. Let us know if you have the good version. 