package main

import (
       "bytes"
       "net/http"
)

func main() {

    headers := map[string][]string{
        // The x-fax-clientid header is required only when using the OAuth2 token scheme
        "Content-Type": []string{"application/json"},
        "Accept": []string{"application/json"},
        "Authorization": []string{"Bearer {access-token}"},
        "x-fax-clientid": []string{"YOUR CLIENT_ID"}
    }

    data := bytes.NewBuffer([]byte{jsonReq})
    req, err := http.NewRequest("POST", "https://restapi.fax.plus/v3/accounts/{user_id}/outbox", data)
    req.Header = headers

    client := &http.Client{}
    resp, err := client.Do(req)
    // ...
}