This seems to be the relevant section excerpted from Green Dot’s T&C:
You may only have one registered Apple Cash Account at a time and, during your lifetime, you may register no more than ten Apple Cash Accounts.
Because your Apple Cash Account is associated with your Apple Account as set forth in Section 1(E) above entitled “Use of the Services Across Eligible Devices”, this means that if you obtain a new Apple Account and attempt to register a new Apple Cash Account under the new Apple Account, you will not be able to do so if you exceed the foregoing lifetime limit, and the Apple Cash Account you attempt to register will be subject to the transaction and account limits set forth in Section 7(B) below entitled “Transaction and Apple Cash Account Limits“ for Apple Cash Accounts that have not been registered.
Source:
https://applecash.greendot.com/termsconditions/