Create API Key
https://support.coingate.com/hc/en-us/articles/4402498918546
Please note, that for "Test" (sandbox) mode you must generate separate API credentials on https://sandbox.coingate.com. API credentials generated on https://coingate.com will not work for "Test" (sandbox) mode.
Provide generated Token to HTTP Authorization Header.
curl "https://api-sandbox.coingate.com/v2/auth/test" \
-H 'Authorization: Token YOUR_API_TOKEN'<?php
$auth_token = 'YOUR_API_AUTH_TOKEN';
$headers = array();
$headers[] = 'Authorization: Token ' . $auth_token;
$curl = curl_init();
curl_setopt($curl, CURLOPT_HTTPHEADER, $headers);