Using the same authenticated session, PS cmlet Get-AzureRmSubscription returns 28 values and the REST API returns 21 (https://management.azure.com/subscriptions?api-version=2016-06-01). The difference in the results is the PS cmdlet returns all the subscriptions across 2 tenant ID's (21+7), whereas the REST API is only returning results for one of the tenant ID's (21).
I don't see any documentation for the REST API call to specify a tenant ID. Is anyone aware of a way to toggle this value, or better yet to return the same results as the the PS cmdlet?