Create a Facebook App
Go to Facebook Developers and click on My Apps on the top-right corner.
Click on Create App
Click on the Business button under Select an app type and click Next
Fill in the necessary details with your business information and click Create app
You might be prompted to enter your Facebook account password on this step.
You will be redirected to your App's Dashboard, here you'll need to scroll down a bit to find WhatsApp. Once you've found it click on Set up
On the top of the page you'll see an App ID, take a note of this number as we'll need it later on.
Select your Meta Business account from the dropdown list and click on Continue
You'll receive a WhatsApp testing number for now. Don't worry, we'll connect your number later on.
That's it! On the next guide we'll connect your current (or new) WhatsApp number. However if you wish you can begin using the test number Facebook provided to begin, bear in mind that the test is limited to 5 contacts though.