Connectivity issue with express-gateway

i have my 3 node containers are running in different networks. also i have customized express-gateway image container running in all 3 networks (bcz it is sending the requests based on APIs.).
i have tried connecting with all 3 containers from express-gateway container shell and its working fine.
but when i try to send the request from postman its showing an error of “bad gateway”.
what am i missing here ?

Hi

Its a bit hard to help without any info.

can you provide the docker run commands / compose files?