Broker endpoint generates 502 Bad Gateway response

[Parisa Moosavinezhad]

I have two Keycloak instances as container on my local machine. 

I configured one of as broker (localhost:8080) and one of the as identity provider (localhost:8081).

When I try to sign in with a user from identity provider the endpoint of the broker generate an error : 502 Bad Gateway.

What should I do to solve the problem?!