How can I approach the idea of building a collaborative payment system? I've built a iOS chat app using Firebase and I'd like to add the functionality of allowing the members of a chat group to contribute an x amount of money where this money can later be utilized by the group admin.
For example, Alice creates a chat group for "Bob's birthday" and adds John and Kareem. They all want to pitch in to buy Bob a gift. John, Kareem and Alice all add $10 each through the "add money" button. Alice takes the $30 and buys the gift.
I've looked into PayPal and Stripe but they all seem to point towards 1-to-1 payments. How can I go about solving this? Thanks.