Prometheus metric not found on server - node.js

Question

I am using the following YAML for my prometheus-adapter installation.
prometheus:
url: http://prometheus-server.prometheus.svc.cluster.local
port: 80
rules:
custom:
- seriesQuery: 'http_duration{kubernetes_namespace!="",kubernetes_pod_name!=""}'
resources:
overrides:
kubernetes_namespace: { resource: "namespace" }
kubernetes_pod_name: { resource: "pod" }
name:
matches: "^(.*)_sum"
as: "${1}_avg"
metricsQuery: "sum(rate(<<.Series>>{<<.LabelMatchers>>}[2m])) by (<<.GroupBy>>)"
This YAML is installed with the following command.
helm upgrade --install prometheus-adapter prometheus-community/prometheus-adapter --values=./prometheus-adapter-values.yaml --namespace prometheus
After generating some load with hey, I tried looking for the _avg metric with the following command.
kubectl get --raw "/apis/custom.metrics.k8s.io/v1beta1" | jq -r '.resources[] | select (.name | contains ("pods/hello_http"))'
This is the output.
{
"name": "pods/hello_http_duration_sum",
"singularName": "",
"namespaced": true,
"kind": "MetricValueList",
"verbs": [
"get"
]
}
{
"name": "pods/hello_http_duration_count",
"singularName": "",
"namespaced": true,
"kind": "MetricValueList",
"verbs": [
"get"
]
}
{
"name": "pods/hello_http_duration_bucket",
"singularName": "",
"namespaced": true,
"kind": "MetricValueList",
"verbs": [
"get"
]
}
Why is the _avg metric not seen? Note that, at the moment, the accuracy of the metricsQuery is not important. I just want to know, why is the _avg metric not seen?
Where do I look for logs? The prometheus-adapter or the prometheus-server logs didn't show anything obvious.
Do I need additionalScrapeConfigs as described here?
This post similar to mine; however, my configuration matches that of OP. What am I missing?