Go to \app\Http\Controllers\OrderController.php
Under the line 350 add this code:
/* START SEND WHATSAPP WITH API TO OWNER AFTER ORDER PLACED*/
//The URL with parameters / query string.
$url = 'https://api.callmebot.com/whatsapp.php?phone=+xxxx&text=xx+xx+xx+xx+xx+xx&apikey=xxxxxx';
//We use file_get_contents to GET the URL in question.
$contents = file_get_contents($url);
/* END SEND WHATSAPP WITH API TO OWNER AFTER ORDER PLACED*/
It is working for me; please let me know if you find any issues.
Regards.-