Hi and thank you for your reply.
I have just testing with “IPN Simulator” and I still get “Invalid” for the IPN_statut. But everything works fine when I make payments via Sandbox. I use your “paypal_ipn_for_wordpress_ipn_response_handler” hook to trigger an action and I obtain the expected result. I finally understood that I had to use the “Custom” field because the session parameters are not usable. Once this is assimilated, your “PayPal IPN for WordPress” plugin appears as a very useful tool: I intend to use it to allow users to buy roles and thus allow them to access certain information. This function exists in the “Advanced Access Management” plugin that I use but it does not work at this time. Well, your extension is of great help to me.