UUI not received from CM for SIP call

[mamb]

Hi,
We are doing a test call/poc to check whether we are able to receive User-to-User (UUI) sent by 3rd party sip dialer and received in TSAPI client application.

setup:
path-1: [sip dialer]-------[Avaya CM-ver-6.0]-------[Avaya CM-ver-5.2]----[Agent VDN]
path-2: [TSAPI client application]-------[AES server]-----[Avaya CM-ver-5.2]

path-1: sip dialer send custom data in SIP header 'User-to-User' & we are able to see in Avaya CM trace (CM MST trace)
But the same is not received in TSAPI Exerciser app & TSAPI client application.

log snippet from MST trace at CM:
==================================
INVITE sip:52347@abc.domain.com:5060;transport=udp SIP/2.0
P-AV-Message-Id: 2_1
Route: <sip:x.x.x.x;transport=tcp;lr;phase=terminating>
Expires: 30
User-to-User: 61626364;encoding=hex

=> all we receive in TSAPI Exerciser is UUI Type: None

we want to receive the UUI data in TSAPI client application but thats not receiving.

In Agent VDN vector step, there is no collect digits & simply route to available agent.
But for testing purpose we havenot logged in any agent for that routing skill.

We made a direct extension call instead of agent vdn and to see UUI is agent phone display, but UUI not displayed.

Is there any configuration missing?
Any step is missing here?
Any configuration to be done in AES?
Please share us on how to troubleshoot & make this work.

Thanks & Regards