As @david55 said, but also note two other issues with the chan_sip implementation:
Item 7 says “Leave this section blank unless you need registration.” but item 10 says “… to ensure it’s registered and functioning properly.”
The offered config shows “host=fixedimsmey.duentdxb.duvoip.fmc”, which conflicts with the problem noted at Request-Line Invite change , which suggests that an outbound proxy is needed.