Golang: invalid character 'U' looking for beginning of value

Question

I'm trying to do a http request which is developed in Golang. when I made a request to retrieve all student data, the data was successfully retrieved. but when I make a request to retrieve student data by ID, I can't retrieve it, I get the following Output:

// fetch all student data
ID: A001         Name:Ipal       Grade:42
ID: B002         Name:Ver        Grade:42
ID: C003         Name:Kris       Grade:42

// fetch student data by Id
 id=B002
payload:  id=B002
request data: &{GET http://localhost:8080/user 
HTTP/1.1 1 1 map[] {id=B002} 0x5f75e0 7 [] false localhost:8080 map[] 
map[] <nil> map[] <nil> <nil> <nil> 0xc00012c020}
DATA-DATA: {  0}
DATA-DATA: {  0}
Data: {  0}
{  0} invalid character 'U' looking for beginning of value
Error! invalid character 'U' looking for beginning of value
2

my student struct script is:

type student struct {
    ID    string
    Name  string
    Grade int
}

my script to fetch all student data is:

func fetchUsers() ([]student, error) {
    var err error
    var client = &http.Client{}
    var data []student

    request, err := http.NewRequest("GET", baseURL+"/users", nil)
    if err != nil {
        return nil, err
    }

    response, err := client.Do(request)
    if err != nil {
        return nil, err
    }

    defer response.Body.Close()

    err = json.NewDecoder(response.Body).Decode(&data)
    if err != nil {
        return nil, err
    }

    return data, nil
}

And here my code to fetch student data by ID:

func fetchUser(ID string) (student, error) {
    var err error
    var client = &http.Client{}
    var data student

    var param = url.Values{}
    param.Set("id", ID)
    var payload = bytes.NewBufferString(param.Encode())
    fmt.Println("", bytes.NewBufferString(param.Encode()))
    fmt.Println("payload: ", payload)

    request, err := http.NewRequest("", "http://localhost:8080/user", payload)
    fmt.Println("request data:", request)
    fmt.Println("DATA-DATA:", data)
    if err != nil {
        // fmt.Println("DATA-DATA:", data)
        return data, err
    }
    fmt.Println("DATA-DATA:", data)
    
    request.Header.Set("Content-Type", "application/x-www-form-urlencoded")
    response, err := client.Do(request)
    if err != nil {
        return data, err
    }

    defer response.Body.Close()

    err = json.NewDecoder(response.Body).Decode(&data)
    if err != nil {
        fmt.Println("Data:", data)
        return data, err
    }
    fmt.Println("Data1:", data)
    return data, nil
}

And here my func main script is:

func main() {
var users, err = fetchUsers()

    if err != nil {
        fmt.Println("Error!", err.Error())
        return
    }
    for _, each := range users {
        fmt.Printf("ID: %s\t Name:%s\t Grade:%d\n", each.ID, each.Name, each.Grade)

    var user1, err = fetchUser("B002")
    if err != nil {
        fmt.Println("Error!", err.Error())
        return
    }
    fmt.Printf("ID: %s\t Name: %s\t Grade: %d\n", user1.ID, user1.Name, user1.Grade)
}

Please Help me Friends