How do i get a password ? Getting exception The input is not a valid Base-64 string as it contains a non-base 64 character...

[Csharper1972]

I'm using the code from the project the WhatsTest
And when i'm running the program i'm getting exception:
On this line:

return Convert.FromBase64String(this.password);

The exception is:

The input is not a valid Base-64 string as it contains a non-base 64 character, more than two padding characters, or an illegal character among the padding characters.

I didn't change the password variable content it's still : static string password = "xLl***************GSA=";
How do i get a new password if i need at all ? And how should i type/add it to the password string variable ?

Thank you.