Configuration of 3CX V12 with grandstream 4224

I have 3CX the soft PBX installed but cannot get the grandstream 4224 gateway good working. internal calls port 1 to port 2 via extension doesnt work at all call from port to ip phone as extension works. (two way audio) call from ip phone to port 1 extension it rings, but when answer no audio when i then put on hook, phone rings again. all on the same network