I'm creating an android application that uses PayPal as a payment method. I have already implemented IPN in PHP but I have some questions about the PDT. From what I understood, the PDT is a notification that occurs when the user pays and returns to the merchant website. My question is, what if the user before being redirected closes the PayPal page? The user never visits the "return page" and I don't receive any immediate notification about the purchase.
I'm selling digital products, so I can't wait for the IPN to allow the user to download the product, as it could take several minutes or even hours to arrive.
What do you think I can do? Do you have any suggestions? Thanks.
PDT and IPN are ~20 years old. PDT in particular is only suitable for informational purposes, since as you mention the user may never return to the redirect page--for any number of reasons. IPN can be relied on but is an asynchronous notification and may delay as you also mention.
The best solution is to use neither of those very old things, and instead capture transactions with a v2/checkout/orders API call. This gives an immediate, synchronous notification when a transaction completes.
Create two routes, one for Create Order and one for Capture Order (first using a function that obtains an access token). These routes should return/output only JSON data (no HTML or text).
Pair those two routes with the following approval flow: https://developer.paypal.com/demo/checkout/#/pattern/server