If you want to have a “chat” button on your website which on Android mobile will directly start the Whatsapp application and send a predefined message to predefined contact number, just copy paste the below lines where ever you need.
<a href="https://api.whatsapp.com/send?phone=91xxxxxxxxxx&text=Hi%20we%20need%20help%20regarding%20something" class="applyinfo-btn">start chat </a>
In above the message we are trying to send is “Hi we need help regarding something”, which when used in html we need to add “%20” for space hence it became as “Hi%20we%20need%20help%20regarding%20something”
For India, it will be 91 as country code in “phone=”, you can check your country code from https://faq.whatsapp.com/en/general/21016748
Refer more at https://faq.whatsapp.com/en/general/26000030