To get a WhatsApp Business API Account you must first pass the Facebook Business Manager Verification process.
To start the verification process go to Security Center and click Start Verification in the Business verification section.
Note: The Start Verification button will be greyed out unless your business needs access to certain features. See the below section on how to enable the button.
If your business is already listed
If your business is not listed
Confirm your business details
Select a phone number that you have access to from the drop-down menu and click Next.
Get a verification code
Choose to receive the verification code on your business phone number via a text message or a phone call or via email. The phone number option may not be available in all countries.
Or verify your domain
If your domain is already verified, click Use Domain Verification. If not, complete the domain verification process, then return to the Security Centre and select Continue.
Enter verification code (not applicable if you use domain verification)
Enter your verification code. Click Submit.
You can SKIP the remaining steps 3 & 5 below.
If you cannot see your business in the list please select None of these match.
Then proceed with the Steps 3 & 5 below.
You may be asked in step 3 to provide official documentation of your business’s legal name. Upload an official document that matches the business’s legal name you entered in step 1.
Documents for legal business name verification
Documents for legal business Address or phone number verification
After you upload the documents, Facebook will review them as quickly as they can. This may take several days. You can check the current status of your verification by going to your Security Center. If you already have a 360dialog account, you can check the status by logging into the 360 Client Hub.
When your business is verified you will be notified and you will also see the verified status in your account.
How can you Verify your Business Manager Account on Facebook when the Verification Button is greyed Out / disabled?
Follow these steps:
In order to enable the "Start Verification" button you must connect a Facebook app ID to your business manager account. In order to do so, first, go to "Facebook for developers"
In the "My Apps" drop-down, if you already have an app click on it or if you don't have an app to create a new one.
Then go ahead and copy the "APP ID" from the dashboard
Click on "Add" and then "Connect an app ID" from the list.
Then go ahead and copy the "APP ID" from the dashboard.
Go back to Facebook Business Manager and check the button. It should now be enabled and you can click on it to proceed with Business Verification.
For more info on the Business Verification Process, please refer to the Official Facebook Documentation on the subject: