Timeout error in ECC "INTERNAL.CLIENT_RECEIVE_FAILED Error while receiving by HTTP (error code: 402 , error text: ICM_HTTP_TIMEOUT)"

Dear Experts,

I am very critical situation due to this timeout error in ECC, please help me as much as you can. Go-live date is very near, but I am not getting any clue why this error is occurring. our ECC system is EHP 4, and PI is dual stack 7.4

My scenario is synchronous ABAP proxy to HTTP_AAE. request is triggering from ECC via proxy and reaching to third party (bank) through PI, I am reviving the response back in PI from bank. But from PI to ECC the response is not reaching. So in ECC after the defined Timeout limit its getting timed out.

I have tried everything by increasing the timeout in ECC more than 15 minutes in HTTP_TIMEOUT under SXMB_adm in ECC, but nothing worked, even if I am increasing for half an hour then also its getting timeout after half an hour.

response from bank to PI is coming within 30 to 40 seconds, but PI is not sending the response back to ECC.

This is classical scenario, and I have checked the trace via SXMB_Moni in PI as well as in ECC, in ECC its showing the timeout error, but in PI i did not see any trace for this error.

I have read many thread on SCN for the same error, and everywhere it has been suggested to increase the timeout, and I have tired that, it didn't help me.

All ABAP proxy configuration has been done as follows.

RFC destinations in ECC

1. LCRSAPRFC(TCP/IP)
2. SAPSLDAPI ((TCP/IP))
3. G type destination to path "/sap/xi/engine?type=entry"
4. G type destination SAP_PROXY_ESR to path "/rep"

All the destination connection test is working fine.

but i have a doubt on G type destination(AAE_XDJ) to path  "/sap/xi/engine?type=entry" which is returns the status code 500 with message "Empty HTTP request received", is it ok with 500 ?

Configuration in ECC Integration Engine configuration is as follows

Questions

1. How the message gets pushed to ECC from PI, once the message received in PI, I believe by G type RFC destination on path  "/sap/xi/engine?type=entry" , please clarify.
2. How to trace this, if message is not getting pushed to ECC, I mean I have checked the trace in PI XSMB_MONI, but didn't get anything for this error. In ECC SXMB_moni only I am able to the timeout error.

Please expert help me as soon as you can, this error really effecting me badly in front of management

Thanks,

Farhan