Eli5: Why does the coin drop after hanging up the pay phone

Question

I always see in the movies that when they hang up a pay phone, you hear a coin drop. What’s the reason for this?

In: 244

Answer 1

When you put in coins they are not automaticalyl dropped to the main hold, because you haven’t used them up. When make a call they gradually drop one by one as you use them up.

When you put down the phone, the coin currently in use is “lost” (you pay for each period started and lose the rest even if you don’t use it up.) The coins not used are given back