An invalid response was received from the upstream server

I have done setup with docker kong. I created one route and service. PFB details:

Route1 : /route1
Service1 : https://mockbin.org/request

We have to note here that upstream url is outside of container.

when I hit request to url http://IP-OF-MY-KONG-SERVER:8000/route1 I am getting below error

{
“message”: “An invalid response was received from the upstream server”
}

On checking logs of kong container, I see below error. Not sure how to fix this issue:

2021/12/09 14:00:53 [error] 1098#0: *53534297 connect() failed (111: Connection refused) while connecting to upstream.

I updated /etc/hosts file of Kong container with ip and domain name of external url but still the same issue.

Please assist.