Because you are using CME I've heard it is a challenge to make fax-passthrough work with VG224 running SCCP.
You can try by configuring following in CME:
voice service voip
modem passthrough nse codec g711ulaw
If that does not work you might have better chance with VG224 running as h323. In this case VG224 will act as h323 gateway. On CME configure incoming voip dial-peer as follows:
dial-peer voice 1 voip
modem passthrough nse codec g711ulaw
fax rate disable
I hope that's a good start.