Why is my Apple Cash under review all of a sudden

Nobody knows and if it is due to suspicious activity that flagged your account, the bank is required to NOT tell you the reason. There are many reasons why that could be the case, but your reason is unknown:

• Commercial use of account
• Identity verification problem
• A person you are sending money to or receiving money from may have triggered an alert
• Dealing with Gambling sites or Crypto sites that violate the terms of use.

In any case Apple has nothing to do with it and GreenDot bank is the one that manages the account and has to abide by the banking regulations of the Bank Secrecy Act and the US Patriots Act without any interference from Apple. You can use the number here to contact GreenDot Bank, but just be prepared that the information provided to you may be limited.

Contact Green Dot Bank by calling (877) 233-8552

I’m assuming you understand that Apple Cash is a Person 2 Person (P2P) service for transferring funds between family and friends. After all, you agreed to the terms and conditions when you opened the account.

Are the recent large payments due to commercial activity on your account? If so, that would definitely be a violation of the T&C.

https://applecash.greendot.com/termsconditions/