Video Upload API only works with 1 file type?

I have a script that uploads a video to an API I built, and after it processes on the API side, a text file is returned to the client. The strange thing is, this only works with one type of file, a .QT file extension. Any other video type I try to send sends and empty video. I have tried .mov, .mp4, and .qt and only the .qt uploads properly. I'll post my code below. Would anyone know what cause only the one file type to work? Nothing on the API side singles out the qt file. I believe this is an issue with this script.

public async void Function() { 

        Debug.Log("works1");
        string filePath = "IMG_0491.mov";
        //string filePath = ProcessMode.theFilePath; 
        var client = new HttpClient();
        

        using (var multipartFormContent = new MultipartFormDataContent()) {
            //Add the file
            Debug.Log("works2");
            

            var fileStreamContent = new StreamContent(File.OpenRead(filePath));

            Debug.Log("works3");

            fileStreamContent.Headers.ContentType = new MediaTypeHeaderValue("video/mov");
            multipartFormContent.Add(fileStreamContent, name: "file", fileName: filePath); //Originally Actual "Name`

            //Send it
            var response = await client.PostAsync("http://127.0.0.1:5000/", multipartFormContent); //Enter IP and Port of API when set up
            Debug.Log("works4");

            //Ensure it was successful.
            response.EnsureSuccessStatusCode();

            //Grab the animation data from the content.
            var animation_data = await response.Content.ReadAsStringAsync();

            Debug.Log(animation_data);
            //Save to file.
            //File.WriteAllTextAsync("AnimationFile.txt", animation_data);
            await File.WriteAllTextAsync("AnimationFile.txt", animation_data);
            Debug.Log("works5");
        }