pypodio2 filter items by known field names and values

I have a field in an app that I am trying to filter by. I can get filtering to work for other fields (though unintuitively). The field I want to filter on is called 'Client/Partner' so my request looks like:

c.Item.filter(app_id, attributes={

Where Foo is the name of a client and it is itself an item from another app. I get the following error:

TransportException(response, data) ... (object): must be array","error":"invalid_value"}

How do I go about grabbing arbitrary items from Podio where I know the name and values of certain fields? The way I thought this works doesn't seem to be working for me. Do I need the 'field id'?