how to send message from whatsapp to custom mobile numbers

Hello Karthik

Please check these links

https://www.c-sharpcorner.com/UploadFile/ansh06031982/send-message-on-whatsapp-number-using-web-service/

https://www.c-sharpcorner.com/UploadFile/c4d11a/sending-whatsapp-message-using-C-Sharp-code/

https://www.c-sharpcorner.com/article/how-to-make-a-whatsapp-messenger-in-C-Sharp-part-2/

https://www.c-sharpcorner.com/article/how-to-make-a-whatsapp-messenger-in-C-Sharp-part-4/

https://www.youtube.com/watch?v=ijscqy3jarc

https://www.youtube.com/watch?v=Z7LedIO47Yw