我正尝试通过API调用将Excel作为附件上传，该API调用需要Excel文件的base64编码版本。通过API成功上传了该文件，但下载时Excel显示一条消息，指出该文件已损坏，无法打开。
我已经尝试了各种不同的payload输出调整。我完全按照API参考文档的要求，文件成功上传。我希望文件应该能够在上传后下载并打开，但我得到了一个损坏的文件。下面是成功上传文件的代码，但似乎没有正确编码文件：
下面是我成功上传文件的现有代码。Payload结构基于API文档：

url <- <api_url>
              
     # Read the contents of the Excel file as a raw object
     excel_file_raw <- readBin(excel_file_path, what = "raw", n =file.info(excel_file_path)$size)
              
     # Encode the Excel file as a base64 string
     file_64_content <- base64enc::dataURI(excel_file_raw,paste0("application/vnd.openxmlformats-     officedocument.spreadsheetml.sheet;name=",file_name), encoding = "base64")
              
      # Define boundary string
      boundary_string <- "-----boundary"
              
      # Create payload
     payload <- paste0("--", boundary_string,
               "\r\nContent-Disposition: form-data; name=\"file\"; filename=\"", file_name, "\"",
               "\r\n\r\n",file_64_content,
               "\r\n--", boundary_string,
               "\r\nContent-Disposition: form-data; name=\"parent\"",
               "\r\n\r\n", task_id,
               "\r\n--", boundary_string,
               "\r\nContent-Disposition: form-data; name=\"resource_subtype\"",
               "\r\n\r\nattachment",
               "\r\n--", boundary_string, "--\r\n")

     # Send POST request
     response <- httr::POST(url,
                     body = payload,
                     add_headers('authorization' = paste0("Bearer ", api_token),
                     'content-type' = paste0("multipart/form-data; boundary=", boundary_string),
                     'accept' = 'application/json'),
                     encode = "multipart")

    # Check API response
    content(response, "text")