Go to the Settings screen through the application menu (Fig. 1) and open the Advanced Settings Screen (Fig. 2).

Fig. 1	Fig. 2

Check Sip Server and Sip Port

Open the SIP settings and check the SIP server and SIP server port

Check username 

Open the SIP settings and check the Username

Check obfuscation

Open the SIP settings and check the obfuscation settings