Odata get 406 not Acceptable error

[a-elnajjar]

We have a problem with Odata get?every time add $select to
URL http://url/Clients?$select=Firstname we have 406 error.
when I add $select=Firstname to URL it goes to else and returns 406 not Ac

public IHttpActionResult Get(ODataQueryOptions<Client> options)
{
    IQueryable queryNew = ODataDynamicPropertyUtilities.ConvertQueryToJsonData<Client>(options.ApplyTo(db.Clients.Include(p => p.ClientTags).ThenInclude(q => q.Tag)));
 
    if (queryNew.ElementType == typeof(Client))
    {
        var results = queryNew.Cast<Client>().ToList();
        return Ok(results);
    }
    //this part cause 406 error 
    else //if (queryNew.ElementType.Name == "SelectSome`1")
    {
        var results = new List<object>();
        foreach (var item in queryNew)
        {
            results.Add(item);
        }
 
        return Ok(results);
    }
 
}

[xuzhg]

The 406 returned is correct because OData can't serialize List<object>().