How can I remove restrictions on my Apple Pay account?

See the following from If Apple Cash is restricted or locked - Apple Support

If your Apple Cash account is restricted

Your account may be restricted if your identity verification fails multiple times, if there are multiple accounts tied to the same social security number, or if there's suspected fraud on the account. If your account is restricted, you can still transfer your Apple Cash balance to your bank or use it to make purchases with Apple Pay. You can't send or receive money, or add money to your account.

If your account is restricted and there are no instructions provided, contact Apple Support.

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