ID greek coin and countermark info

Hello everyone.

I came across this coin, which seem to have a countermark or something similar.
Can you tell me what it is?

If you could also help me identify it, I’d be really grateful.

3.46 grams / 16.8 mm

Thank you very much.

Is there any expert?

Hi,

Reverse is really worn and obverse with apollo head can be found in many coins, I thought I've recognized this Antandros coin N#469161 but the weight is not matching.

Will keep searching and some real experts may help as well.

Best

Hub

Thank you. Yes, the reverse it's really worn.

Maybe the countermark could be a useful hint?

The countermark can indeed be a clue as countermarks were stamped onto foreign coins using a punch in order to give them legal tender status in a city. Countermarks were most often used to give a coin a new value or to allow worn coins from the same city to continue to circulate. 
There are many countermarks, so here is an example to look at: https://www.coinarchives.com/a/results.php?results=100&search=countermarks 

Thank you for the explanation. Very useful indeed.

I will have a look.