Hi Mou,
What is the Current PI version for which you are sending message ?
If you are using classical configuration then sender channel should be with XI adapter , In case you are using ICO then the channel has to be SOAP with XI 3.0 message protocol
and in both case your sender agreement(classical config) / ICO header should have the below details.
Sender system: MEBCLNT500
Sender interface : XXXXX'
Namespace : http://'YYYYYY
It would be helpful if you put screenshot of your PI configuration (sender agree or ICO).
Regards,
Manoj