You could transfer them the money then send them a request for the same amount of funds. If sent money requests start appearing in the Share section of the app, then you’d be able to keep track of the unpaid amount there.
You can vote for the ability to track pending money requests here:
Alternatively, you could transfer them the money and then set up a Shared Tab to track their repayments:
- Create Shared Tab and add the amount they owe you as a custom bill.
- Every time they pay you some of it back, you can add another custom bill to reduce the amount they owe.