I have not. Historically, the Pro unlock will work for all versions in a series, i.e. Pro version 6 will work in all versions in the 6 series. I got my Pro version 7 at about 7.2.x, and it has worked fine with all through version 7.5.5, where I am now. The current version is 7.6.6, and I have heard of no issues with a Pro version 7 unlock not working in any versions later than my 7.5.5.
Seems strange, but then maybe Apple has departed from history?
I will GUESS, since the OP does not provide details, that the QT key he has won't work 'cause he's trying to apply it to a different version entirely, not just a .(dot) upgrade within a version
If his key is for QT6 or QT5 it will, of course, not work in QT7
That would be an issue. Apple gets my US$ 30 with every series upgrade, though it does last for the dot upgrades, within that series.