The event shop for the Madoka collab shop functions differently from the regular event shops. It uses an event currency called Purple Crystals which can be obtained via the Event Stage First Clear Rewards, Event Missions, Event Box Gacha, and rolling on the collab banners.
The shop has two tabs. The first tab will be available immediately once the collab event starts. You will be able to exchange for skill and Exclusive Armament upgrade materials for the Madoka units [excluding Mami and Homura (Glasses)] as well as where you can exchange your pity ticket from the collab banner for your desired unit.
It takes 8560 Purple Crystals to clear out the first tab of the event shop, so you were not able to clear it as a F2P in CN and JPN, but the developers promised to change how the shop works in the Global version. We're currently waiting for the details.
The second tab will only unlock after you have purchased all of the items in the first tab that has a purchase limit and contains mainly regular upgrade material. The only unique item in the second tab is Regular Recruitment Order (the currency used in the AG Direct Hiring Shop).
Event Shop Gacha
In addition to the event shop, the Madoka collab also has an event box gacha that will give rewards
To pull on the box gacha, you must expend Silver Coins to draw out a random reward from the pot. Each draw costs 10 Silver Coins. Silver Coins can be obtained by defeating the Event Boss.
There are 7 boxes total. At the start, you will only be able to pull rewards from Box 1. To unlock Box 2, you will need to pull all of Box 1’s “jackpot” prizes first. The rest of the boxes are also unlocked using this process where you have to obtain all of the “jackpot” prizes of the previous box first before the next one unlocks. You can always go back to a previous box and continue to pull rewards from that box.
The rewards Box 1 through 6 are one-time only. However, Box 7 is an infinite box where the rewards inside of the box will reset after you have completely cleared it out.