sip 77

Hello,I need to use a SIP account to receive calls on an extension of my Asterisk. I am using the AsterisNow, and set up through the FreePBX. If I set up my account at any Voip device I can receive calls without problems, but with account configured on Asterik not receive calls. When making calls with SIP same account I have no problems, only to receive is the problem. Then describe the ... hsi ushul tsalatsah halaqah 77