Unable to connect to page

hello people, I have this issue with a web page response.

I have configurate a connection with a gateway pay and all it works for moment.
When I am starting the proccess to do the pay and entry the credit card value, the operation finish succesfull, but when the bank try to send the response data on my response page (Transferencia de vehículos | Trámites DGT Online) the same connection is fails with code 404 “fail to send response to merchant”

payment documentation: https://desarrolladores.addonpayments.com/#!/hosted-payments/pay-by-link

the documentation says:
> Once payment is complete, HPP will return the transaction response to a nominated URL that can be supplied in the POST (MERCHANT_RESPONSE_URL). The response will contain a hashed string (SHA1HASH field) made up of key transaction variables, including the Order ID, Result Code and Timestamp. This must be constructed and checked by your application to ensure the response has not been tampered with, please refer to our Process a Payment documentation

My dounbt: on the response page, is missing something to recive? in other words, I need declarate some parameters on the url to obtain the information respond?

thanks a lot!!