To fetch metrics details of File systems of AWS EC2 Instances, the fs name must be passes as well in the parameters to get metrics.
The call would use the following template: arn:aws:ec2:{region}:{owner-id}:instance/{instance-id}:fs/{fs_name}
Below is an example of a request using this template:
https://chapi.cloudhealthtech.com/metrics/v1/?&asset=arn:aws:ec2:us-east-1:<owner-ID>:instance/<instance-ID>:fs/<FS name attached to Insatnce>'