If theres a coin in there then you should be able to remove it using a pair of pilers.
But if you cannot remove it from there then you will need to remove the pump. To do this pull the washer out and lean it backwards against a wall.
Then remove the plastic kickstrip and then you can see the screws holding the pump on.
Remove these and then you can drop the pump down and then just give it a shake and the coin will come out from there.
Then refit the pump and retry it and see how it goes from there and let me know.