Webmoney API

<form action="https://merchant.webmoney.ru/lmi/payment.asp" method="POST">
    <input type="hidden" name="LMI_PAYMENT_AMOUNT" value="{PAYMENT_SUMM}">
    <input type="hidden" name="LMI_PAYMENT_DESC_BASE64" value="<?=base64_encode('Тестовый платеж')?>">
    <input type="hidden" name="LMI_PAYEE_PURSE" value="{WMID}">
    <input type="hidden" name="LMI_PAYMENT_NO" value="{TEST_MODE (1 - test 0 - production)}">
    <input type="submit" class="wmbtn" style="font-famaly:Verdana, Helvetica, sans-serif!important;padding:0 10px;height:30px;font-size:12px!important;border:1px solid #538ec1!important;background:#a4cef4!important;color:#fff!important;" value="&#1086;&#1087;&#1083;&#1072;&#1090;&#1080;&#1090;&#1100;0.05.00 WMZ ">
</form>

// Проверка платежа (ответ от webmoney)

$_POST['LMI_SECRET_KEY'] = {SECRET_KEY};

$strArray = [
    $_POST['LMI_PAYEE_PURSE'],
    $_POST['LMI_PAYMENT_AMOUNT'],
    $_POST['LMI_PAYMENT_NO'],
    $_POST['LMI_MODE'],
    $_POST['LMI_SYS_INVS_NO'],
    $_POST['LMI_SYS_TRANS_NO'],
    $_POST['LMI_SYS_TRANS_DATE'],
    $_POST['LMI_SECRET_KEY'],
    $_POST['LMI_PAYER_PURSE'],
    $_POST['LMI_PAYER_WM']
];
$hash = strtoupper( hash('SHA256', implode('', $strArray)) );
if($_POST['LMI_HASH'] === $hash){
// С платежом все ок! здесь все остальные проверки
}