Why
In order to start sending WhatsApp messages to customers you are required to add a payment method to your WhatsApp account. Even if you already have an existing credit line with Meta (for Facebook or Instagram ads), you still need to configure your payment separately.
How
Important: you need a meta business manager admin access before you can configure your payment method.
Go the business manager
In the left menu click on settings
Click on WhatsApp accounts under Accounts
Select your WhatsApp account
Click on Payment Settings
Now click on Add payment method