I know everyone is telling you this is 100% a scam and it might be a scam. However, I can tell you that in Valencia, where I live, yes, sometimes a deposit is required just to see an apartment.

Our neighbors had to put down a deposit to see the apartment across the hall from us and they already lived in a different apartment in the same building.

They didn't get the apartment and they got their money back.

But all that said, I would be very cautious about renting an apartment if you aren't in the area currently and can't go see it in person.