Graph API with filter ref properties does not seem to work as documented

Question

I am calling Graph API
https://graph.microsoft.com/v1.0/groups/{id}/members?$count=true&$filter=startswith(displayName, 'a')

with header ConsistencyLevel: eventual

and getting a result of
request_unsupportedQuery
the specified filter to the reference property query is currently not supported

yet it is documented here as to work
https://learn.microsoft.com/en-us/graph/api/group-list-members?view=graph-rest-1.0&tabs=http#example-5-use-filter-to-get-group-membership-with-a-display-name-that-starts-with-the-letter-a-including-a-count-of-returned-objects

What is the issue?

Best,
Aapo

Answer 1

I was missing $count=true.
Sorry.

-Aapo

Answer 2

If I remove the filter, I am getting expected results.