I have three keys that came with my used Walking Dead (Pro) pin. (Pictures below)

-Two keys are identical (stamped "Suzo-Happ E21"). These open the coin door. They will also fit into the backbox lock, but they won't turn/unlock the backbox.

-The third key is different. It's flat on one side and is stamped "Suzo-Happ 510". It does not fit into the coin door or backbox. I have no idea what this key is for.

There are no additional keys hanging inside the coin door or in the coin box.

Questions:
-What is this third key for? Is there a lock on the machine I'm not seeing?
-Should my coin door key also unlock my backbox? Or are they keyed differently?
-Are these three keys the keys that would have come NIB with the machine?
-Is picking the backbox lock my best option?

The manual has no information regarding keys and I couldn't locate any posts asking this very novice question.

I really appreciate the help!
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Sorry, I should have been more clear. I purchased the game yesterday from a private seller (HUO) who bought it NIB in 2014. These three keys, all on the same keychain, is what the seller gave me.

I will ask, but I strongly doubt the seller has any additional keys lying around. I wouldn't be surprised if he never personally opened the backbox at all, as by his own admission he never had the machine serviced. So he may have not even known the third key did not work on anything.

Also, yes, it was incredibly foolish of me to not open the backbox prior to purchasing. I feel terrible about it.

Thank you, everyone, for the replies. I will look into all of these suggestions.

I think this random third key may always be a mystery!

Nope. I looked everywhere around the door twice, had someone else look as well, and checked everywhere on the floor of the cabinet.

Edit: Previous post I said their were no hooks. There are definitely hooks, but no keys.

Hey, just wanted to follow up on this specific suggestion. I just got back from a local locksmith / key maker store, based off me sharing with him the images I shared above -- which show the lock (H95) and the key that fits but does not turn (E21) -- he was not able to make a key for me that fit. He wants me to bring in the physical key (E21) for the coin box and he will see what he can do. Didn't sound too promising. -- Appreciate the suggestion though!

I think I'll end up either picking the lock, or buying several Suzo Happ "H95" keys and see if any of them fit.

Thanks. I just snapped these pictures of mine. I now notice the hooks, which of course, do not have keys on them.

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LTG Would you be able to tell me if your backbox lock and keys have H95 stamped on them? Your keys look similar to these ones on amazon --- which I might just order. Thanks!

https://www.amazon.com/Double-Bitted-Cabinets-Drawers-Pinball/dp/B07B9PYFN2/ref=sr_1_fkmrnull_2

That would be amazing, thank you. I'll PM you.