.net core 2.1 "POST" an IFormFile using Postman - the application completed without reading the entire request body

Try doing it like this. Use the same request in postman you are using now. This is just crude boilerplate method but you get the idea.

Also, dont forget to set headers of your request in postman to: Content-Type: multipart/form-data

[HttpPost]
[Route("api/image")]
public async Task<IHttpActionResult> InsertNewMerchant()
{
        // your form data is here
             var formData = HttpContext.Current.Request.Form;
             HttpFileCollection files = HttpContext.Current.Request.Files;


            if (files.Count == 1)
            {
            // this is the file you need 
                var image = files[0];
                    // do something with the file
            }
    return StatusCode(System.Net.HttpStatusCode.Created);
}

I found the solution for .Net Core 2.1/2.2 here

POST multiple files from POSTMAN

POST single file from POSTMAN

    [HttpPost]
    public async Task<IActionResult> UploadSingleFile([FromForm(Name = "file")] IFormFile file)
    {
        if (!ModelState.IsValid)
            return BadRequest(ModelState);
        var IDsList = new IDsList();

        try
        {
            var id = SaveFile(file);
            IDsList.Files.Add(new IDsList.FileInfo() { id = id, fileName = file.FileName });
        }
        catch (Exception ex)
        {
            return BadRequest(ex.Message);
        }

        return Content(JsonConvert.SerializeObject(IDsList), "application/json");
    }

    [HttpPost("UploadFiles")]
    public async Task<IActionResult> UploadFiles([FromForm(Name = "files")] ICollection<IFormFile> files)
    {
        if (!ModelState.IsValid)
            return BadRequest(ModelState);

        //var files = Request.Form.Files?.GetFiles("files");
        String message = String.Empty;
        int filesCounter = 0;
        var IDsList = new IDsList();

        foreach (var file in files)
        {
            if (file.Length == 0)
                message = message + $"errorDescription {file.FileName}\n";

            try
            {
                var id = SaveFile(file);
                IDsList.Files.Add(new IDsList.FileInfo() { id = id, fileName = file.FileName });
                filesCounter++;
            }
            catch(Exception ex)
            {
                message = $"{message}{ex.Message}\n";
            }
        }

        IDsList.message = $"Amount: {filesCounter}.\n{message}";

        return Content(JsonConvert.SerializeObject(IDsList), "application/json");
    }

Seems like there is an error problem with Postman macOS application. When I'm using the postman chrome extension everything works as expected.

MacOS app

Chrome extension