Verify your identity to continue to use Apple Cash

Tap "Verify Identity." According to: Identity verification for Apple Card or Apple Cash - Apple Support

"When you'll be asked to verify your identity

You'll be asked to verify your identity based on how much you use Apple Cash. You may not add or receive $500 or more in total without verifying your identity. You might also be asked to verify your identity prior to this limit.

To protect your account and the security of your money, you might be asked to verify your identity when using Apple Cash, even if you have previously done so."