Firstly you have to signup for TWILIO  

A third-party service that connects you to your real-time customers, through WhatsApp. After signup, you can see a dashboard seen below. First, copy Account SID and Auth token and click on the button shown in the image below 

After that you can see this page click Messaging

After clicking on the Whats App  setting  you can see a new view as shown in the image below place this Url 
https://gtchatpro.com/whatsapp/received 
in both fields of configurations and copy your whats app number 
 

After that place your Account SID  and Auth token  and this Whatsapp number in your admin dashboard profile section as shown in the image  

After clicking edit button you can see this 

Now you can see your WhatsApp here and ready to go