controller.cs

[HttpPost("{bucketName}"), DisableRequestSizeLimit]
        public async Task<IActionResult> UploadFile([FromRoute]string bucketName)
        {
            var file = Request.Form.Files[0];
            
            var response = await _service.UploadFileAsync(bucketName, file);

            if (response.Status == System.Net.HttpStatusCode.OK)
            {
                return Ok(response);
            }
            else
            {
                return BadRequest(response);
            }
        }

services.cs

public async Task<S3Response> UploadFileAsync(String bucketName, IFormFile file)
        {
            try
            {
                var transferRequest = new TransferUtilityUploadRequest()
                {
                    InputStream = file.OpenReadStream(),
                    AutoCloseStream = false,
                    BucketName = bucketName,
                    Key = file.FileName,
                    StorageClass = S3StorageClass.Standard
                };

                transferRequest.Metadata.Add("Date-UTC-Uploaded", DateTime.UtcNow.ToString());


                await new TransferUtility(_client).UploadAsync(transferRequest);

                return new S3Response()
                {
                    Message = "File Uploaded",
                    Status = System.Net.HttpStatusCode.OK
                };
            }
            catch (AmazonS3Exception e)
            {
                Debug.WriteLine(e.Message);
                return new S3Response()
                {
                    Status = System.Net.HttpStatusCode.BadRequest,
                    Message = e.Message
                };
            }
            catch (Exception e)
            {
                Debug.WriteLine(e.Message);
                return new S3Response()
                {
                    Status = System.Net.HttpStatusCode.BadRequest,
                    Message = e.Message
                };
            }
        }