PayPal IPN simulator - how to generate INVALID response?

Question

I'm using Paypal IPN simulator to test changes. I'm trying to generate an INVALID response.

I select

Transaction type: Cart Checkout

payment_status: Denied, Failed or Expired.

However all of these generate a notification call with response VERIFIED

update didn't read close enough. Documentation says: PayPal sends a single word back, which is either VERIFIED if the message originated with PayPal or INVALID if there is any discrepancy with what was originally sent. So if I just browse to my IPN URL directly, I will get an INVALID response from Paypal because the call to IPN did not originate with PayPal.

Answer 1

Regarding your update: close, but not exactly.

IPN will return VERIFIED or INVALID depending on whether or not it recognizes the POST data you're sending as having originated from PayPal.
So yes, if you browse to your IPN URL directly and it directly POST's no data / dummy data to PayPal, then yes, we won't recognize it as having originated from us and we'll return INVALID.

For example, this link will return INVALID: https://www.paypal.com/cgi-bin/webscr?cmd=_notify-validate&dummy_data=true