If you're having trouble connecting your WhatsApp business account to your Facebook page, here are some common reasons:

• The verification code was input incorrectly: Make sure you entered the correct verification code.
• Your code is correct, but the verification code expired: The verification code is only valid for a short amount of time. If you need a new verification code, select Send another code.
• The phone number you sent a verification code to is not connected to a WhatsApp business account: Make sure you have created an account on the WhatsApp Business app, and that you entered the correct number linked to the account.
• You never received a verification code: If you never received a verification code to your phone number, select Send another code during the account verification process.

* Nguồn: Facebook