Check Your Payment Method
Verify that your WhatsApp Business Account (WABA) has a payment method attached. Without one, you cannot send template messages.
Steps
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Go to business.facebook.com and sign in with an account that has full access to your Business Portfolio.
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In the left panel, click your Business Portfolio and open Business Settings (gear icon).

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Click WhatsApp Accounts in the left sidebar, then select your WABA.
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Find the Payment Method section — it should show a credit card or bank account.

If no payment method is listed, see Add a Payment Method.