locating reports that use a particular dataflow

I'm a Power BI admin and I'm trying to identify reports that are using a particular dataflow.  Doesn't seem to be a way to go from the dataflow to the reports, so this looks like I could use the upstreamDataflows REST API: https://docs.microsoft.com/en-us/rest/api/power-bi/admin/datasets_getdatasettodataflowslinksingroupasadmin

When testing using a workspace with a report/dataset where my developers tell me they are using a known dataflow, the "value" comes back blank.  Am I querying something incorrectly?  Is there a different way to do this I haven't found yet?  I am able to query for reports and datasets, but this one comes back blank.  Have others used this successfully?  

If you're interested... my Powershell query:

$url = 'admin/groups/' + $workspace.Id + '/datasets/upstreamdataflows'

Invoke-PowerBIRestMethod -url $url -Method Get