When you make a booking with split payment, you actually don’t need to add any players at the time of booking. You can later go into the booking and share a link with your friends so they can join the match. For example, if you send the link to a group with more members, the first three players who click on the link and pay will join the match.

You will find the link on the bookings page in the app. Press the three dots in the top right corner and choose "share booking".