Now that MCOC has its own brand new web store, I'm guessing a lot of people are going to be looking for it very soon, when the Summer sales for 2023 start up. Here is where it is located:
https://store.playcontestofchampions.comHOWEVER. DO NOT TRUST ME OR ANYONE ELSE TO GIVE YOU THIS LINK DIRECTLY
It is far too easy to set up a fake store site then attempt to lure players to it. Since you have to log into it, they can harvest your login credentials and then do all sorts of nasty things. If you go far enough, they can also harvest your payment information. That's worse.
So what should you do? Here's DNA's four part safety procedure for using the web stores for players who are concerned about online safety (which should be everyone).
One: Do not click on links to the store posted in public areas. No No No No No No No. It doesn't matter if you think you recognize the link.
For those unwilling to take this advice, here's the link to the store again:
https://store.playcontestofchampions.com(note: the link is a safe demonstration of the principle)
Do not trust links from untrusted sources. They are a convenience, but when safety matters they are also a hazard.
Two: Do link to the store from a known official site.
The official game site is playcontestofchampions.com. The site name is the same as the forum domain name, without the "forums." In the upper right hand corner is a site menu, and that site menu has a link to the web store:

Alternatively, type the name in yourself. The name of the site is the same domain name of these forums, just replace "forums." with "store." And if you do, double check for typos. Triple check for typos. One way fraudsters try to capture victims is to set up nearby domain names. If you accidentally type playcontestofchamps.com instead of playcontestofchampions.com and you just assume you typed the right thing because "it worked" you might have accidentally landed on a fraudulent site instead.
Three: Verify that you are connected to the right site name with SSL.
In other words, you should be going to https:// and not
http://. Also, verify that when you do, the SSL certificate for the site is valid. That's the little lock icon that most browsers have.

If you are not connected SSL or that lock isn't present, do not use the site. And if you aren't sure if the lock is locked or not, every browser has their own version of clicking on the lock and double checking:

You want to drill into that and see this:

Secure connection, valid certificate. Anyone can make up a fake site. It is a lot harder to forge valid digital certificates that will be valid for the correct domain names.
None of this will help if an attacker hacks the actual store. There I can't offer a four part easy way to keep yourself secure. But don't make yourself an easy target. It isn't easy to hack online stores. It is really easy to just ask you for your passwords and payment info and have you hand it over. Don't do that.
And finally, Four: use credit cards whenever possible on the web store.
The web store offers payment options from (believe it or not) Apple Pay to debit cards to freaking Chuck E Cheese (no, that's not a joke). But my advice is: use credit cards. They are your last line of protection against fraud. If you do not get the items you purchased, and you believe you were suckered into a fraudulent site, you can always revoke the transaction and attempt to get a refund. My recommendation is if you realize you went to the wrong place, revoke the transaction immediately. If you think you went to the right place and everything was fine but you did not get the items in a timely manner, open a support ticket. If Kabam support says they have no record of the transaction, *then* revoke the transaction immediately.
I recognize not everyone has this option, and in fact you may be trying to use the web store specifically because you want alternate payment options. If so, see the first three recommendations above. However, if credit cards are an option, I always recommend them for internet transactions.
Remember, if you hand your money to some total stranger who claims to be Kabam, Kabam can't help you. They can't refund money they didn't get. They can't give you the items you didn't pay for, even if you have otherwise lost the money. The in-game store is still the safest option, but if you're going to use the web store, and there might be advantages to using the web store, do so carefully. I do not want to be responding to forum posts next week from people who lost their money to scammers and want to know what they can do about it. There is very little they will likely be able to do about it.