Asterisk Now integration with GXW-8004 Grandstream VOIP GW

Hello,
We are stuck within an Asterisk Now integration with GXW-8004 Grandstream VOIP GW , here`s our scenario:
We have one Asterisk Now server having already 3 FXO lines installed on it , plus we have adeded 4 PSTN lines that we ahev connected to GXW-8004 Grandstream VOIP GW as FXO lines.
Asterisk is already working with the prevous 3 PSTN FXO lines , while adding the new VoIP GW : GXW-8004 , we are facing the following problem , all the outgoing calls from the extension 103 configured on SIP server and VOIP GW are working but do not go through the 4 PSTN lines installed on the GXW Gateawy , besides the status of the FXO lines is showing Not registered on the GXW-8004 GW.
Could you pls help us configure this setup.
regards,
Mondher