In order to submit a WhatsApp Business API application, you need to have a verified business account on Facebook. For more information, check out our Requesting Access article.
Verification is easy to obtain, but sometimes, your Start Verification button in Facebook Business Manager will be disabled, like this:
Follow this guide in order to enable it.
Log into the Facebook Developers page and click "Create App", you can name it whatever you like, it doesn't matter.
That should generate an App ID (found in the top header). Copy the App ID from the top left:
Go back to the Business Settings page in your Business Manager, on the left side menu, select Business Settings → Accounts → Apps.
Click "+ Add".
Enter/paste your App ID from the previous step and refresh the page.
That's it! Your Start Verification button should now be activated in your Security Settings page. Click the button to initiate the process.