My g729 codec proven working

This is when my elastix IPPBX passing g729 codec to my a2billing and my a2b finally can accept it. Otherwise a2billing will provide below error

[Dec 24 10:15:50] NOTICE[2706] chan_iax2.c: Rejected connect attempt from X.X.X.X, requested/capability 0x4/0xc incompatible wit
h our capability 0xe100.

debiana2b*CLI> iax2 show channels
Channel Peer Username ID (Lo/Rem) Seq (Tx/Rx) Lag Jitter JitBuf Format
IAX2/7425593609-1355 X.X.X.X 7425593609 13557/02718 00015/00016 00040ms -0001ms 0000ms g729