Apple Cash Overdrawal

What happens if the Apple Cash account becomes overdrawn?

A recent purchase from a Square terminal that included a tip temporarily processed without the tip, resulting in the available Apple Cash balance being higher than what it should be. Later that day, I paid the balance on my Apple Card, which pulled all of the available balance from the Apple Cash account, leaving it at $0. Without any other deposits, the final posting of the Square transaction (including the tip) would have left the Cash balance negative.

Fortunately, I noted this issue and added funds to Apple Cash before the final amount with the tip processed.

So it appears possible that this quirk could result in an overdrawn Apple Cash account. If so, what would happen?