payment.php

<?php
//Please modify the following variables
$amount = '250'; // E.g. "250" for 2.50 EUR!
$currency = 'EUR'; // ISO 4217
$description = $_SERVER["HTTP_REFERER"];
$privateApiKey = 'TESTPRIVATEKEY';

if (isset($_POST['paymillToken'])) {
    $token = $_POST['paymillToken'];

    $client = request(
        'clients/',
        array(),
        $privateApiKey
    );

    $payment = request(
        'payments/',
        array(
             'token'  => $token,
             'client' => $client['id']
        ),
        $privateApiKey
    );

    $transaction = request(
        'transactions/',
        array(
             'amount'      => $amount,
             'currency'    => $currency,
             'client'      => $client['id'],
             'payment'     => $payment['id'],
             'description' => $description
        ),
        $privateApiKey
    );

    $isStatusClosed = isset($transaction['status']) && $transaction['status'] == 'closed';

    $isResponseCodeSuccess = isset($transaction['response_code']) && $transaction['response_code'] == 20000;

    if ($isStatusClosed && $isResponseCodeSuccess) {
        echo '<strong>Transaction successful!</strong>';
    } else {
        echo '<strong>Transaction not successful!</strong> <br />';
    }

    echo "<pre>";
    var_dump($transaction);
    echo "</pre>";
}

/**
 * Perform HTTP request to REST endpoint
 *
 * @param string $action
 * @param array  $params
 * @param string $privateApiKey
 *
 * @return array
 */
function requestApi($action = '', $params = array(), $privateApiKey)
{
    $curlOpts = array(
        CURLOPT_URL            => "https://api.paymill.com/v2/" . $action,
        CURLOPT_RETURNTRANSFER => true,
        CURLOPT_CUSTOMREQUEST  => 'POST',
        CURLOPT_USERAGENT      => 'paymill-paybutton-example/1.2.0',
        CURLOPT_SSL_VERIFYPEER => true,
    );

    $curlOpts[CURLOPT_POSTFIELDS] = http_build_query($params, null, '&');
    $curlOpts[CURLOPT_USERPWD] = $privateApiKey . ':';

    $curl = curl_init();
    curl_setopt_array($curl, $curlOpts);
    $responseBody = curl_exec($curl);
    $responseInfo = curl_getinfo($curl);
    if ($responseBody === false) {
        $responseBody = array('error' => curl_error($curl));
    }
    curl_close($curl);

    if ('application/json' === $responseInfo['content_type']) {
        $responseBody = json_decode($responseBody, true);
    }

    return array(
        'header' => array(
            'status' => $responseInfo['http_code'],
            'reason' => null,
        ),
        'body'   => $responseBody
    );
}

/**
 * Perform API and handle exceptions
 *
 * @param        $action
 * @param array  $params
 * @param string $privateApiKey
 *
 * @return mixed
 */
function request($action, $params = array(), $privateApiKey)
{
    if (!is_array($params)) {
        $params = array();
    }

    $responseArray = requestApi($action, $params, $privateApiKey);
    $httpStatusCode = $responseArray['header']['status'];
    if ($httpStatusCode != 200) {
        $errorMessage = 'Client returned HTTP status code ' . $httpStatusCode;
        if (isset($responseArray['body']['error'])) {
            $errorMessage = $responseArray['body']['error'];
        }
        $responseCode = '';
        if (isset($responseArray['body']['data']['response_code'])) {
            $responseCode = $responseArray['body']['data']['response_code'];
        }

        return array("data" => array(
            "error"            => $errorMessage,
            "response_code"    => $responseCode,
            "http_status_code" => $httpStatusCode
        ));
    }

    return $responseArray['body']['data'];
}