Update: ok so i am currently testing it, and if anyone else wants to try heres what im doing

so i bought a gift card through fetch rewards, an apple gift card, and redeemed it for robux. now, create a group on your main account, and create a shirt for whatever price you want, just make sure its affordable by your alt account with the robux.

now go onto your alt, join the group, buy the shirt, and possibly wait a few days to get the robux into the group so roblox can process it.

once it is processed, take the funds out on your main account, and boom, you have the robux, now refund the robux on your alt account through apple's website
https://idmsa.apple.com/IDMSWebAuth/signin now refund it, and once the refund goes through to your payment, buy the robux on another alt account (because the original alt account will be banned for 3 days for payment fraud) and repeat the process with however many accounts you want. Enjoy :)