Custom metrics shows a 404 error

Summary

Displaying the custom metrics list and adding new custom metrics from the Prometheus integration settings page does not work.

Workaround:
Create a cluster with Environment Scope *.

Steps to reproduce

• add a Kubernetes cluster at group level
• configure Prometheus using Manual configuration
• in the project, go to Settings -> Integrations -> Prometheus

What is the current bug behavior?

The error message "Error: Request failed with status code 404" is displayed in place of the custom metrics list.

Trying to add a new custom metric displays "There was an error trying to validate your query" even if the query is valid.

The System metrics (Kubernetes) (pods memory and CPU usage) are working correctly.

The 404 error from the metrics list seems to come from a GET request to the following URL: https://gitlab.com/<group>/<project>/prometheus/metrics

The query validation error also seems to be a 404 error to the following URL: https://gitlab.com/<group>/<project>/prometheus/metrics/validate_query

Relevant logs and/or screenshots

Output of checks

This bug happens on GitLab.com