Installed whatasppp Business api followed the link https://developers.facebook.com/docs/whatsapp/installation
Logged into https://localhost:9090/
For registration, it requires a phone number and a certificate.
Setup the Whatsapp Business APP for phone number then added the number in Facebook business manager.
However, couldn't acquire the cerificate to complete the registration. There are instructions in the link https://developers.facebook.com/docs/whatsapp/api/account but couldn't follow it, there is no settings tab or whatsapp manager button to acquire the certificate as mentioned in 3rd point.
Useful Links
Embedded
https://www.facebook.com/business/help/2640149499569241
Direct - Intended for people developing applications for themselves or their organization
https://developers.facebook.com/docs/whatsapp/cloud-api/get-started
Verification
What you're looking at on Facebook Business Manager is the WhatsApp account for your WhatsApp Business App. This is the 'WhatsApp for Business' app account that you can download from Google Playstore or Apple AppStore. In order for you to create and use WhatsApp Business API account, you need to create an api account. You can reach a Business Solution Provider to help you setup an account. More details can be found here on WhatsApp's official page.
Here is the list of BSPs provided on their website.