Golang API Post upload file - go

Question

I'm new to golang and I'm trying to write a function that uploads a file with a post request to API server. I try Post API in Postman, it is OK but in my code I have some error like this image
This is my golang code:
func (c *Client) PostUploadFile(endpoint string, params map[string]string) []byte {
url := "/examples/image/text.txt"
body := &bytes.Buffer{}
writer := multipart.NewWriter(body)
// Open the file
file, err := os.Open(url)
if err != nil {
// return nil, err
}
// Close the file later
defer file.Close()
part, err := writer.CreateFormFile("file", filepath.Base(url))
_, err = io.Copy(part, file)
if err != nil {
fmt.Println(err)
// return nil, err
}
for key, val := range params {
_ = writer.WriteField(key, val)
}
err = writer.Close()
if err != nil {
// return nil, err
}
fmt.Println("Data request:")
fmt.Println(body)
fmt.Println("Endpoint:")
fmt.Println(c.BaseUrl + endpoint)
req, requestErr := http.NewRequest("POST", c.BaseUrl+endpoint, body)
if requestErr != nil {
log.Fatalln(requestErr)
}
req.Header.Add("auth_token", c.AuthToken)
req.Header.Add("accept", "application/json")
// req.Header.Add("Content-Type", "application/json")
req.Header.Add("Content-Type", writer.FormDataContentType())
client := &http.Client{}
fmt.Println("Response:")
resp, err := client.Do(req)
fmt.Println(resp)
if err != nil {
log.Println(err)
return []byte(``)
}
return c.parseBody(resp)
}
and this is a param formdata in body:
fmt.Printf("%+v\n", c.UploadImage(map[string]string{
"file": "/examples/image/text.txt",
"wfs_id": "30578",
"id": "59284",
"element_id": "119726",
}))