<?php

    if(isset($_POST['generatePayment'])) {
        $shopId             = intval(111);
        $description        = strval('Opłata za fakturę');
        $control            = strval(1234576948);
        $price              = floatval(100);
        $notifyURL          = strval('xxxxx');
        $returnUrlSuccess   = strval('xxxxx');
        $hash               = 'hash';

        $data   = $hash . "|" . $shopId . "|" . sprintf("%.2f", $price);

        if ($control != null && $control != "") {
            $data .= "|" . $control;
        }

        if ($description != null && $description != "") {
            $data .= "|" . $description;
        }

        if ($notifyURL != null && $notifyURL != "") {
            $data .= "|" . $notifyURL;
        }

        if ($returnUrlSuccess != null && $returnUrlSuccess != "") {
            $data .= "|" . $returnUrlSuccess;
        }

        $signature = hash('sha256', $data);

        $paybylinkData  = [
            'shopId'            => $shopId,
            'price'             => $price,
            'control'           => $control,
            'description'       => $description,
            'notifyURL'         => $notifyURL,
            'returnUrlSuccess'  => $returnUrlSuccess,
            'signature'         => $signature
        ];

        $data_string = json_encode($paybylinkData);

        $ch = curl_init('https://secure.pbl.pl/api/v1/transfer/generate');
        curl_setopt($ch, CURLOPT_CUSTOMREQUEST, "POST");
        curl_setopt($ch, CURLOPT_POSTFIELDS, $data_string);
        curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
        curl_setopt($ch, CURLOPT_HTTPHEADER, array(
            'Content-Type: application/json',
            'Content-Length: ' . strlen($data_string))
        );

        $result = curl_exec($ch);
        $result = json_decode($result);

        if(isset($result->transactionId) AND !empty($result->transactionId)) {
            header('https://secure.pbl.pl/transfer/' . $result->transactionId)
        } else {
            echo 'Wystąpił błąd.';
        }
    }
?>

<form method="post">
    <input type="hidden" name="generatePayment">
    <input type="submit" value="Zapłać">
</form>