Remove Contacts from Lists Bulk Activity api error

I'm trying to remove one contact from one list via the Bulk Activity API.

I get this error:

400 Bad Request: [[{“error_key”:“contacts.api.bad_request”,“error_message”:“source[list_ids] is empty, list_ids, contact_ids are mutually exclusive”}]]

My JSON payload only sends the one contact id that I want to remove from the list:  (note that the quotes around the attribute names and values don't show up--they aren't there in the objects but apparently get added by the Spring Rest Tempate--I've had success calling other CC V3 API endpoints with this Java client). 

 {
    source: {
        contact_ids: [e19f3996-6e48-11ec-ac92-fa163e963dae]
    },
    list_ids: [24337c6e-6da8-11ec-b55c-fa163e470cab]
}