I believe you copied that code from this thread, too: whatsapp - C# How to send messages with whatsapi.net? - Stack Overflow
Basically, WhatsApp has no password, this is a requirement of the API written for WhatsApp communication. Also, from the first answer it is clear that you need to send your own phone number to get the code. Then use that as the authentication medium. I am not sure, but this thing (kind of) sounds like OAuth methods for authentication and authorization.
Pankaj, on that thread, shared a code that works,
WhatsApp wa = new WhatsApp("your number", "your password", "pankaj", false, false);
wa.OnConnectSuccess += () =>
wa.OnLoginSuccess += (phno,data) =>
wa.OnLoginFailed += (data) =>
The problem with these methods and mechanisms is that these APIs are all third-party and they lack proper documentation for the objects and methods. WhatsApp themselves don't have an API because they don't store the data on their central server. To have an API, it would require you to store a miniature server on every device. I did write this in another thread, and I can't find that... Sorry.
OAuth - Wikipedia, the free encyclopedia