Nice! I have two Caligula provincials... apparently of the same type (not the one in the OP, but from a different client kingdom).
Funnily, I had the first one unidentified for quite a while (considered posting it on CCF, but couldn't get a good photo), and then bought the second one (in a different place) because I read "Germanikos" on it and (correctly) guessed that it meant the coin must have been from the 1st century.
Then, the day I figured out the second coin, I happened to stumble on the first, and went "wait, that looks familiar"... lo and behold, it was the exact same type (and even part of the "Germanikos" legend was visible).
That said, the two coins are extremely different in size and, especially, weight - so much, in fact, that attributing them to the same type feels weird.
I really should post that pair on CCF eventually. I think I even made some photos - I just need to pass them through the optimizer.