When you pay for something, it is the serial number code or installation number you are paying for.
This should be written down in three places, one of those places being a red piece of paper taped to the ceiling.
If you registered this product, the manufacturer should have the code.
Yeah, I know, and I did. Trouble is, I've made so many moves in the interim, and had enough computers (1 Mac & 2 PCs) die on me that whatever safe place I chose to store that info has gone the way of the dodo and the passenger pigeon. Looks like I'll just have to keep using the Mac alone for FMP 5 chores, until such time as I see a need to buy the current version (and since I'm still running OS 9.2 on the Mac, I suspect the most current versions of FMP won't work there either).