Is This A Celtic Drachm?

Hi everyone,
I just acquired this nearly uniface drachm-like coin. It is 3.45g and 17mm in diameter.
The reverse appears to have a standing image of Poseidon with one foot on an object and holding a trident. Some Greek text appears to the right of the trident.

The obverse, however, has almost no detail. There is only a bulbous blob that sort of resembles the shape of a dead. Thus, it is very reminiscent of some very late-stage dies of Celtic drachms and tetradrachms.

Do you suspect that this is a Celtic Drachm? Given the detail of the standing figure and accompanying text on the reverse, is there any way of knowing which Greek city state this coin may be emulating? Thanks!