Grandstream GXW4108 FXO Gateway Export required.

Looking for Grandstream expert/ VoIP engineer who can fix call connectivity billing problem. The details are as follow we have Grandstream GXW4108. It's FXO Gateway. We want to use this gateway as PSTN gateway it means VoIP call will enter in Grandstream GXW4108 and will hit PSTN FXO lines for call out. We have made all settings. But we have 1 problem. When caller is calling from VoIP to Grandstream GXW4108. It's ringing twice at caller end(PC 2 Dialer) and on 3rd ring showing status call connected leg A billing is starting(onPC 2 Dialer). But on other side leg B side is still ringing and no billing starting at leg B(on Grandstream Gxw4108) . We want to solve this issue, Support for Grandstream Gxw4108 settings VoIP to Grandstream GXW4108 is required.