Buying MtX doesn't usually cross over like it does for Fortnite?
Epic can run a sale where they offer 30% off vbucks on their digital store on a web browser but keep it non discounted anywhere else (30% is the cut that consoles take). They can make their store look more attractive and encourage the adoption if their digital storefront.
Look at Apex Legends for example, you can cross play, but you do not have cross progression . Your battle pass rank does not share and your coins stay platform locked.
Look at Outriders, you can cross play. The game currently doesn't have MTX, but you still can't cross progression. You must make a new character if you want to play on PS5 from a pc.
Destiny 2 allows you to cross progression, but restricts Silver to the platform you purchased it on.
In Fortnite , your skin unlocked on ps4 transfer to PC. The vbucks you buy stay on their console you purchased them on (ps, switch, pc/mobile, xbox), but unlocking a skin in your account make it available everywhere. This is not typically available for crossplay games.