var whatsappUrl ="whatsapp://send?phone=$phone";
await canLaunch(whatsappUrl)? launch(whatsappUrl):print("open whatsapp app link or do a snackbar with notification that there is no whatsapp installed");
Intent intentWhatsapp = new Intent(Intent.ACTION_VIEW);
String url = "https://chat.whatsapp.com/<group_link>";
intentWhatsapp.setData(Uri.parse(url));
intentWhatsapp.setPackage("com.whatsapp");
startActivity(intentWhatsapp);