Adding Attachment to Trello card using the API

Question

I am currently making an API call where I am trying to attachment a file from my system to trello using the API, if i go via postman and attachment my file using form data in the body it attaches successfully, but when I try to do it using my code it gives me a 400 Bad request. Here is my endpoint:

    public async Task<IActionResult> AddCard([FromForm] IFormFile file)
{
    if (file == null || file.Length == 0)
    {
        return BadRequest();
    }
    CardModel result = await _trelloRepository.AddAttachment(file);

    return Ok(result);
}

and this is my service where the error is occuring:

public async Task<CardModel> AddAttachment(IFormFile file)
{
    HttpClient client = new HttpClient();
    try
    {
        string AddCard = String.Format("https://api.trello.com/1/cards/{0}/attachments?key={1}&token={2}", "610c13f817940f7daf32dc2a", key, token);
        var myContent = System.Text.Json.JsonSerializer.Serialize(file);
        var buffer = System.Text.Encoding.UTF8.GetBytes(myContent);
        var byteContent = new ByteArrayContent(buffer);
        byteContent.Headers.ContentType = new MediaTypeHeaderValue("application/json");
        HttpResponseMessage httpResponse = await client.PostAsync(AddCard, byteContent);
        string content = await httpResponse.Content.ReadAsStringAsync();
        return content;

    }

I noticed when using the trello api in postman I had to name the form data request as file because when i named it something like image, it did not work