Kubernetes ingress-nginx call service from non-default namespace

I have 3 services in my ingress, the first 2 use default namespace. The third service is prometheus-server service which has namespace ingress-nginx.
Now, I want to map my prometheus DNS to the service, but getting error because ingress can’t find the prometheus service in default namespace.

How to deal with non-default namespace in ingress definition?

Source: StackOverflow