C# Blazor, ExcelDataReader Memory Stream gives Invalid Signature, FileStream does not

Trying to figure out why I am unable to read a MemoryStream using ExcelDataReader. If I hard code the path to the CSV file and pass the stream as a FileStream it works. My problem is that I am getting the file from Blazor using <InputFile OnChange="LoadFile" accept=".csv,.xlsx,.xls" /> which only provides me an IBrowserFile, which gives me a Stream, not a FileStream. When I attempt to pass this in the following code (which works on this file if I pass a FileStream) I get an "Invalid Signature" exception.

The code:

using (var memoryStream = new MemoryStream()){    System.Text.Encoding.RegisterProvider(System.Text.CodePagesEncodingProvider.Instance);    // Copy the file data to the memory stream    await browserFile.OpenReadStream().CopyToAsync(memoryStream);    memoryStream.Position = 0; // Reset stream position to the beginning    var config = new ExcelReaderConfiguration    {        FallbackEncoding = System.Text.Encoding.UTF8 // Default encoding    };    // Exception happens here, CreateReader...    using var reader = ExcelReaderFactory.CreateReader(memoryStream, config);    var result = reader.AsDataSet(new ExcelDataSetConfiguration()    {        ConfigureDataTable = _ => new ExcelDataTableConfiguration()        {            UseHeaderRow = true // Use the first row as column names        }    });}

The body of the exception is:

ExcelDataReader.Exceptions.HeaderException  HResult=0x80131500  Message=Invalid file signature.  Source=ExcelDataReader  StackTrace:   at ExcelDataReader.ExcelReaderFactory.CreateReader(Stream fileStream, ExcelReaderConfiguration configuration)   at CollectXScore.Web.Utilities.ExcelCSVFileReader.<LoadFile>d__1.MoveNext() in mycode.cs:line 44  This exception was originally thrown at this call stack:    [External Code]

When make the call this way it works for the same file:

FileStream source = File.Open("C:\\myfilepath\\" + browserFile.Name, FileMode.Open);using var reader = ExcelReaderFactory.CreateReader(source);

What am I doing wrong?