1930 indo-china 20 cents Error coin? ID +value

Was about to sell this to a friend, but I had a funny feeling about it so I kept it. Put it under lens and sure enough, there is an issue. Can anyone help to identify the error, a grade on the coin, and if the error adds value and if so how much? Thanks a lot.

P.S. I only see an error on the date, so am I missing more issues? If not, then how does a coin only get an error on one spot like that?

Looks like a double die but I have no idea about the value

Does doubling traditionally raise the value on foreign silver? Or is this not a severe enough case?

I'm sorry but I don't know the answer to that question because I don't collect errors and I have never owned one.