Research the API that the following providers have:
https://www.facebook.com/business/partner-directory/search?platforms=whatsapp&solution_type=messaging&sort_by=alpha

We must integrate the said API with the existing whatsup services that we have.

Twilio documentation

https://www.twilio.com/docs/sms/whatsapp/api#using-phone-numbers-with-whatsapp

WhatsApp vitrifaction process for twilio number:

1. Get the Facebook Business Account verified. Check your business information at https://business.facebook.com/settings/info, under Business Verification Status. If the account is showing “Unverified”, it will also show a link to get verified. Follow the process, and verify your account. More information about the verification process can be found here.
2. Once the account is verified, open a support ticket with Twilio, requesting to apply to a WhatsApp Official Business Account with the following information: Screenshot showing your verified account status, the Business Website Address, the Facebook Page URL, and business name in languages other than English (if any). We will use this information to open a ticket with WhatsApp to get the account verified.

It typically takes up to 2 weeks to get an account verification review completed.

Twilio/WhatsApp and  facebook page business manager registration process.
https://www.twilio.com/docs/sms/whatsapp/tutorial/connect-number-business-profile 

Other whatsApps partners that are investigate are the follow:

• https://www.hubtype.com
• https://www.infobip.com/products/whatsapp-business 
• https://www.tyntec.com/whatsapp-business-api
• https://chat-api.com/en/sdk/csharp.html