PayPal instant payment notification warning

Hi,

I got a mail from PayPal called and there is:

You should check the server that handles PayPal instant messaging. IPNs sent to the following URLs fail:
https://mysite.com/wc-api/WC_Gateway_PPEC/

[where is mysite is my name site]

I am using the PayPal checkout plugin.

I also have the standard on the payment methods on WooCommerce, but this is not active on my website.

Please, help