Appending JSON struct to JSON file Golang

I have a JSON document of Users where they have an ID#, Phone#, and Email. Upon input of another ID, Phone, and Email, I want to take a new user's information and append it to the file. I have a structure that only contains an {ID: #, Phone: #, Email: #} and that's working fine. But my JSON file becomes as such:

[{"ID":"ABCD","Phone":1234567890,"Email":"johndoe@test.com"}]
[{"ID":"EFGH","Phone":1234567890,"Email":"johndoe@test.com"}]
[{"ID":"IJKL","Phone":1234567890,"Email":"johndoe@test.com"}]
[{"ID":"MNOP","Phone":1234567890,"Email":"johndoe@test.com"}]
[{"ID":"QRST","Phone":1234567890,"Email":"johndoe@test.com"}]
[{"ID":"UVWX","Phone":1234567890,"Email":"johndoe@test.com"}]

So I'm able to append to the document, but it's a new JSON structure enclosed by brackets []. Below is my code. I omitted the actual hashed ID.

func ToIds(e string, p int64) {
    hashed := GenId()
    var jsonText = []byte(`[
	    {"ID": "", "Phone": 0, "Email": ""}
    ]`)
    var I Identification
    err := json.Unmarshal([]byte(jsonText), &I)
    if err != nil {
	    fmt.Println(err)
    }
    I[0].ID = hashed
    I[0].Phone = p
    I[0].Email = e

    result, error := json.Marshal(I)
    if error != nil {
	    fmt.Println(error)
    }

    f, erro := os.OpenFile("FILE_PATH", os.O_APPEND|os.O_WRONLY, 0666)
    if erro != nil {
	    fmt.Println(erro)
    }

    n, err := io.WriteString(f, string(result))
    if err != nil {
	    fmt.Println(n, err)
    }

}

This may be of use, here is my Identification struct.

type Identification []struct {
ID string
Phone int64
Email string
}

Essentially, I want the outside brackets, and inside those brackets I want to append multiple users. Something like this:

    [
    {"id":"A", "phone":17145555555, "email":"tom@gmail.com"},
    {"id":"B","phone":15555555555,"email":"p@gmail.com"},
    {"id":"C","phone":14155555555,"email":"bradley@gmail.com"},
    {"id":"D","phone":17135555555,"email":"g@gmail.com"},
    {"id":"E","phone":17125555555,"email":"ann@gmail.com"},
    {"id":"F","phone":17125555555,"email":"sam@gmail.com"},
    {"id":"G","phone":14055555555,"email":"john@gmail.com"},
    {"id":"H","phone":13105555555,"email":"lisa@gmail.com"}
    ]

To achieve your output, define struct as follows-

type Identification struct {
   ID    string
   Phone int64
   Email string
}

And perform operation as follows-

// define slice of Identification
var idents []Identification

// Unmarshall it
err := json.Unmarshal([]byte(jsonText), &idents)

// add further value into it
idents = append(idents, Identification{ID: "ID", Phone: 15555555555, Email: "Email"})

// now Marshal it
result, error := json.Marshal(idents)

// now result has your targeted JSON structure

Sample program of above explanation https://play.golang.org/p/67dqOaCWHI