Vatsal, note that since the is a map that can list several pvcs, it should be provided as one.
Therefore instead of:

"volumes_attributes" : {"name":"gluster-default-volume", "capacity":"1"}

The expected is:


"volumes_attributes": {
  "0": { "storage_class": "gluster-default-volume", "capacity": "1"}
}


With recent fix, if capacity is not provided, an exception will be thrown with a clear message.

vatsal, 
According to the error, you are using a wrong subnet ID:
Key (subnet_id)=(2) is not present in table "subnets"

please, try again with subnet id that exists.

I suppose the needinfo was meant for vatsal, not me.

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://access.redhat.com/errata/RHSA-2019:3172