How to make IPN to send only one time request for payments
I'm trying to use IPN in paypal api. I've created https://ipnpb.sandbox.paypal.com/cgi-bin/webscr ; but every time i use postman to send the approval request , i get the response in IPN endpoint. how to make PayPal IPN to send me only once or keep sending till the server receive it then the IPN stop sending this specific payment for the user. NOTE: when i try using IPN simulator i get this message "ipn was not sent and the handshake was not verified. review your information."
but I receive the data in my back-end server. so is there something wrong in my code logic ?