0a63cdc4 this might help

src/mod/endpoints/mod_sofia/sofia.c

@@ -6088,6 +6088,11 @@ static void sofia_handle_sip_i_state(switch_core_session_t *session, int status,
 					switch_channel_set_variable(channel, SWITCH_ENDPOINT_DISPOSITION_VARIABLE, "DELAYED NEGOTIATION");
 				} else if (switch_channel_test_flag(channel, CF_PROXY_MEDIA)) {
 					switch_channel_set_variable(channel, SWITCH_ENDPOINT_DISPOSITION_VARIABLE, "PROXY MEDIA");
+					switch_core_media_patch_sdp(tech_pvt->session);
+					if (sofia_media_activate_rtp(tech_pvt) != SWITCH_STATUS_SUCCESS) {
+						nua_respond(nh, SIP_488_NOT_ACCEPTABLE, TAG_END());
+						switch_channel_hangup(channel, SWITCH_CAUSE_INCOMPATIBLE_DESTINATION);
+					}
 				} else {
 					if (sofia_media_tech_media(tech_pvt, (char *) r_sdp) != SWITCH_STATUS_SUCCESS) {
 						switch_channel_set_variable(channel, SWITCH_ENDPOINT_DISPOSITION_VARIABLE, "CODEC NEGOTIATION ERROR");