Get project requirements via SOAP

I want to get the requirements for a project using the SOAP interface and hoped that I could do something like this in C#,

var requirements = _client.Requirement_Retrieve(new RemoteFilter[] { new RemoteFilter { PropertyName = "ProjectId", IntValue = 23 } }, 0, 9999);

But according to https://www.inflectra.com/Support/KnowledgeBase/KB88.aspx there is no project id or name to filter on.

Is there another way of doing this without getting all the requirements and filtering them manually.