The serial number was typically printed on the original CD sleeve or a sticker on the capture device itself.
Even if your serial passes verification, Honestech TVR 2.5 likely on Windows 10 or 11. The reasons:
If you're still stuck, I can help you set up an alternative. Let me know: What are you using? Which version of Windows is on your computer?
Because the algorithm is client-side, it is technically possible to generate a valid key for any name using a keygen—but again, that is legally gray.