Hi crowmadame,
Thanks for posting on Apple Support Communities. I understand that suddenly you are unable to transfer your Apple Cash balance to your bank account. First, I would suggest to Restart your iPhone and verify that iOS is up to date: Update your iPhone, iPad, or iPod touch. Then go back to your Apple Wallet and see if you can transfer funds now.
One reason this can happen is if your account has been locked. Have you received any alerts or know if the account has been locked recently? This article explains restricted or locked accounts in more detail. If your Apple Cash account is restricted or locked.
Otherwise, this article has several other troubleshooting steps to help. Transfer money in Apple Cash to your bank account or Visa debit card. Specifically reference the section titled If you can't transfer money.
If you still are experiencing this issue please don't hesitate to Contact Apple Support.
Cheers!