Apple Cash Family - "Family member already has Apple Cash enabled"

I'm attempting to set up Apple Cash Family in a family sharing group. I experience an issue when attempting to add a minor (under 18 years of age), telling me that Apple Cash is "already enabled" on their account. However, Apple Cash does not show as enabled on their device - further, attempting to turn it on from their device (for a personal Apple Cash account) says that they do not meet the age requirements. How can I find and disable this "already enabled" account?

This can happen if the minor has previously created an Apple Cash account but was unable to verify it due to not meeting the age requirements. The account does not show up because it is not active, it cannot be enabled because they do not meet the age requirement, and yet it prevents them from having an Apple Cash Family card created on their behalf.

To resolve this issue, you can call Apple Pay support at (877) 233-8552. Once they verify the minor's identity, they will be able to close the empty account so that you can create a new one.