I’ve looked everywhere to find out what the url is for the PayPal IPN. I’ve only found instructions on how to set it up via PayPal and vague instructions on the notification url is.
 
I did this on a WordPress website. Basically I created a blank page called IPN and set the notification url to it. For example: https://mywebsite.com/ipn
 
You can find the full instructions here:
https://support.weltpixel.com/hc/en-us/articles/115006119347-How-to-fix-PayPal-Instant-Payment-Notification-IPN-Warning-SOLVED-