Understanding PayPal’s IPN notification warning
What is a PayPal IPN notification warning?
IPN is a service that notifies you about updates to your PayPal transactions. Fundraise Up doesn't utilize this service, so if you receive such a notice, it was likely triggered by another third-party tool interacting with your PayPal account.
For more information about PayPal IPN, please visit PayPal's FAQ, and their help center guide for Why did I get an email with the subject "PayPal Instant Payment Notification Warning"?