How to issue the goods after payment?

Question

Node.js

I use this method of receiving payment on the site
https://merchant.webmoney.ru/conf/guide_simple.asp
After successful payment, the buyer is directed to the success page.
How can I send the goods to the buyer after successful payment?
Shipping will be by post.
Is there any way for me to check the payment status? But I don’t even know what payment ID will be assigned, because from the form I get directly to the payment page without the ability to set an ID from my store.
Here is the payment form:

<form id=pay name=pay method="POST" action="https://merchant.webmoney.ru/lmi/payment.asp" accept-charset="windows-1251" >
    <p>пример платежа через сервис Web Merchant Interface</p>
    <input type="hidden" name="LMI_PAYMENT_AMOUNT" value="1.0" />
    <input type="hidden" name="LMI_PAYMENT_DESC" value="тестовый платеж" />
    <input type="hidden" name="LMI_PAYMENT_NO" value="1">
    <input type="hidden" name="LMI_PAYEE_PURSE" value="Z145179295679" />
    <input type="hidden" name="LMI_SIM_MODE" value="0" />
    <input type="submit" value="submit" />

</form>

Answer 1

You should read the documentation: https://merchant.webmoney.ru/conf/guide.asp#properties
Namely, about the Result URL parameter, to which the callback will come, which will need to be processed.

Answer 2

First money - then chairs... words by O. Bender.