Grandstream config

Can anyone help me with a config for a Grandstream GXP-2xxx series phone? My system has endpoint manager, and my Grandstreams all picked up the “outbound proxy” setting and works perfectly fine without STUN or NAT traversal set to STUN.

A separate system I’m involved with is having lots of one-way audio issues, which I know is usually a NAT issue, so I’m using NAT Traversal = STUN with as the STUN server but it doesn’t seem to be helping. I’m wondering if the outbound proxy setting is causing STUN not to work properly.

I’m not using Endpoint Manager but maybe this will help? On the account page of the Grandstream phones I have:
Use DNS SRV - no
User ID is phone number - no
SIP Registration -Yes
Unregister on reboot - no
Support Sip Instance ID - no
Register Expiration - 60
local SIP port 5060
SIP Registration failure retry wait time 30
SIP T1 Timeout 1 sec
SIP T2 Interval 4 sec
SIP Transport UDP
Use RFC3581 Symmetric Routing - no
NAT Transversal (STUN) No
Subscribe for MWI - no
Subscribe for Registration event - no
Publish for presence - no
Voice Mail UserID *97
Send DTMF via RTP (RFC2833)
Early dial - no
skipping down a bit to Vocoder
SRTP Mode -disabled

Don’t know if that helps at all but I thought I’d give it a shot.