With German coins, what I have found is that every coin I've looked for from 1700 to now is in Numista, but before 1600, it's common for the coin to not be listed. But you can add it.
https://en.numista.com/help/a-coin-a-banknote-or-a-piece-of-exonumia-is-missing-in-the-numista-catalogue-what-can-i-do-8.html
I'm not sure why the other reply says that you can't sell on this platform. It's true, but people ask about how much a coin would sell for all the time. The answer depends a lot on the condition of the coin, so a picture would help. But nobody is going to give a definitive answer for a coin that's worth anything. What you can do is look the condition of your coin, and what similar coins have sold for.