Marketplace (like depop) Checkout Functionality


I’m currently creating a marketplace app, kinda like depop but specific to a certain niche.

I’m having trouble creating a checkout system, whereby buyers can add multiple items to a cart from different seller, but can only checkout ONE sellers items (but want an option for multiple item checkouts from that seller) at once, like on depop.

Any insight on how to do this would be great!!

Many thanks,
Ton Mazzone