I am working on a custom payment system for my blog (PHP), and now I am trying to implement the IPN system. I have fully copied the PayPal php example, but no matter what I do, I always get an INVALID response when validating the IPN request. I have read tons of other topics explaining the same problem and still can't find a solution. - I am using the OFFICIAL code example - I am using the sandbox IPN address - I have tried with and without setting a value in 'payment_date' , because many others suggested that the problem is in the plus sign inside the date. - Tried with and without https:// at my end - I have tested the code on 2 different servers, from 2 different PayPal developer accounts. And each and every time the response of the validation is INVALID. I am almost ready to give up... Thanks in advance!
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