Wrong IP WebSocket

Hello Everybody,

wondering if anybody could help with the following issue:
I have a FreePBX up and running and correct ports forwarded from my Public IP to FreePBX private IP ( When using Windows Based sip clients, I have no issues.
When I try to use (from internet) sipml5 using WebSocket (Enabled on FreePBX box, not using webrtc2sip) running on another box (local ip in the same lan as the FreePBX box), I am getting RTP Packets send to incorrect IP:

recv=SIP/2.0 200 OK
Via: SIP/2.0/WS df7jal23ls0d.invalid;rport=33468;received=79.123.AA.BB;branch=z9hG4bKoAKrTaEcA5XZ3UCDdzXfGytev
From: "1001"sip:[email protected];tag=d5u3pfsfmp5Ka327kT
To: sip:*[email protected];tag=as56e183c9
Contact: sip:*[email protected];transport=WS
Call-ID: c10dd797-9620-b435-3a9e-13db536dcdb2
CSeq: 50484 INVITE
Content-Type: application/sdp
Content-Length: 579
Server: FPBX-2.11.0(11.4.0)
Supported: replaces,timer

o=root 1008714939 1008714939 IN IP4 91.AAA.BBB.CCC
s=Asterisk PBX 11.4.0
t=0 0
m=audio 12482 RTP/SAVPF 0 8 101
a=rtpmap:0 PCMU/8000
a=rtpmap:8 PCMA/8000
a=rtpmap:101 telephone-event/8000
a=fmtp:101 0-16
a=candidate:Hc0a8c8e8 1 UDP 2130706431 12482 typ host
a=candidate:Hc0a8c8e8 2 UDP 2130706430 12483 typ host
a=crypto:0 AES_CM_128_HMAC_SHA1_32 inline:W4pd+xM8TiFMNrtgastV/AEeTWFypijJqj32yw

I am assuming, it must have been FreePBX telling to the Client, to which IP to send the RTP Packets. Otherwise I do not see how else it could find out the Private address of my FreePBX box.

The Question is obvious: How to make it work?