1. Log into your paypal click the summary icon from the top menu:

2. From the left menu, scroll down and select 'Seller Preferences'.

3. When the screen loads, select 'Instant Payment Notifications'.

4. Click to 'Edit Settings' and enter the url to the 'paypal.php' file in your lockbox root. This should be done ONLY if no url currently exists. Example:
https://www.example.com/lockbox/paypal.php (Replacing the domain/path with your own correct path. Note that you MUST use https and have valid SSL certificate installed)

Make sure the radio button to 'Receive IPN Messages' is selected and click 'Save'. Note that if you already have an IPN url specified for another system, this does not need changing. This should
be all you need to activate IPN for your website. Note that you must have a premier or business account for this to function correctly.
Paypal is now ready to go.