The new MCOC web store has an interesting feature. Based on location data, the web store will present you with a list of payment options. Some of those are obvious: Apple Pay, Google Pay, Amazon Pay, credit card, etc. But then there are some weird ones: CVS, 7-11, even (for some people) Chuck E Cheese. What the heck are those options about?
Most of those are actually ways to pay in-person for the stuff in the store. You could pay by credit card, by debit card, even by cash. But before anyone uses this option, here's what I learned from doing tests on the process.
First, when you buy something from the web store and select one of those payment options, the game will give you essentially an invoice to pay. For me this came in the form of an email from "PayNearMe.com" (different locations might have different processors).

When you are ready, you hit the Pay Now button, you pick a location to pay at, and you get a barcode the store can scan as if it was an item to buy:

If they know what they are doing, they just scan the code and you just pay the bill. It takes between five and fifteen minutes for the transaction to clear (at least in my testing) and then the items are delivered to your account just like with any other purchase.
Pretty straight forward, but what if you pay cash? Well, everything is the same with one twist: there's no way to refund cash.
One thing I decided to test is whether the web store enforced purchase limits. Consider: you can "buy" an item and you get an invoice. Until you pay it, you haven't actually bought the item yet. So what happens if you then instant-buy the item from the store using, say, Apple Pay. You get the item immediately. But now what happens if you take the invoice to the appropriate store and attempt to buy the item again?
Turns out, at least in my testing, the web store accounts for this. If you have already bought the item and reached the purchase limit, you can't buy it again. The transaction will fail. Then what?
Xsolla can't refund cash, so instead it grants you a credit towards your next purchase. However, at the moment this happens rather invisibly. The system doesn't directly tell you this happened. You can trace transactions and receipts, but it isn't obvious. In particular, there's a separate site operated by xsolla (the company that built and operates the web store) called Babka. If you register for a Babka account you can see all of your xsolla transactions, whether they succeeded or failed, and store credits if any.
Credits are automatically applied to the next purchase you make. So if you have ten bucks of credits and you try to buy a 25 dollar thing, the price will actually show as 15 dollars. It doesn't actually say "25 dollars minus 10 dollar credit." It just says 15 dollars.
I actually don't know what xsolla does if you pay in-person by credit card. I don't know if they reverse the charge or if they give you credits. I'm inclined to believe the latter, but I'm not sure. If you're going to pay by credit card anyway, why not just do that on the store instead of in person. Regardless, be aware that failed transactions can happen, and if they happen you might get store credit instead of refund, and this is definitely true for in-person cash transactions.
For those wondering where the web store is, I direct you to my post on that subject:
https://forums.playcontestofchampions.com/en/discussion/339638/psa-heres-where-the-web-store-is-but-dont-take-my-word-for-it