REST API 401 Unauthorized Error on record collection filtering but simple searches work

I appreciate any help here. I've tried everything I can think of. I've compared the Postman requests and C# requests, but not seeing anything.

I have several simple search queries. Searches by Id or getting all results works great and everything works fine in Postman. However, with my C# code any record collection filtering gets the 401 error.

Here is some sample code to reproduce it:


internal async void TestSearches()

{
//string query = "nonInventorySaleItem";  // Works

//string query = "nonInventorySaleItem/12885";  // Works

//string query = "nonInventorySaleItem?q=itemId CONTAIN ABC123";  //Gets a 401 Unauthorized
string query = "nonInventoryResaleItem";  //Works

//string query = "nonInventoryResaleItem/7517";  //Works

//string query = "nonInventoryResaleItem?q=itemId IS 32305";  // Gets a 401 Unauthorized