User
  constructor(accountId: String = "", userId: String = "", msisdn: String = "", jwtToken: String = "", deviceId: String = "", displayName: String = "")
Parameters
account
Client's account id
user
User's unique identifier used to identify the callee when placing a call.
msisdn
User's phone number.
jwt
JSON Web Token that works as an authenticator token on server side.
device
Unique identifier provided by FirebaseInstanceId.
display
To be used to send to callee as the user name.