curl -X GET "https://api.example.com/api/v1/customers" \
  -H "Authorization: Bearer mk_test_1234567890abcdef" \
  -H "Content-Type: application/json"

fetch('https://api.example.com/api/v1/customers', {
  headers: {
    'Authorization': 'Bearer mk_test_1234567890abcdef',
    'Content-Type': 'application/json'
  }
})
.then(response => response.json())
.then(data => console.log(data));

import requests

url = "https://api.example.com/api/v1/customers"
headers = {
    "Authorization": "Bearer mk_test_1234567890abcdef",
    "Content-Type": "application/json"
}

response = requests.get(url, headers=headers)
print(response.json())

package main

import (
	"fmt"
	"net/http"
	"io/ioutil"
)

func main() {
	url := "https://api.example.com/api/v1/customers"
	req, _ := http.NewRequest("GET", url, nil)
	req.Header.Add("Authorization", "Bearer mk_test_1234567890abcdef")
	req.Header.Add("Content-Type", "application/json")

	res, _ := http.DefaultClient.Do(req)
	defer res.Body.Close()
	body, _ := ioutil.ReadAll(res.Body)

	fmt.Println(string(body))
}

<?php
$ch = curl_init();

curl_setopt($ch, CURLOPT_URL, "https://api.example.com/api/v1/customers");
curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
curl_setopt($ch, CURLOPT_CUSTOMREQUEST, "GET");

$headers = array();
$headers[] = "Authorization: Bearer mk_test_1234567890abcdef";
$headers[] = "Content-Type: application/json";
curl_setopt($ch, CURLOPT_HTTPHEADER, $headers);

$result = curl_exec($ch);
if (curl_errno($ch)) {
    echo 'Error:' . curl_error($ch);
}
curl_close($ch);
echo $result;
?>