Depending on your PayPal account type, you should see a select for “Seller Preferences” on your main page. This will likely be on the left hand side under a menu heading “Selling Tools.” Click on “Seller Preferences” to get to the Seller Preferences screen.
This should give you your account profile. One of the line options should say “Instant payment notifications” with a link to update your settings.
When you click update, you will have a screen that indicates your IPN settings. Make sure IPN is turned on! If there is no notification URL, or it does not match the location indicated in the extension’s subscriptions tab, click edit settings and add this location in the Notification URL box. The image below shows these two screens. Again, make sure you’ve entered the correct IPN listener location for notifications and that you have enabled IPN messages.