IPN sent to the following URL failed

I am having a email come through Please check your server that handles PayPal Instant Payment Notifications (IPN). IPNs sent to the following URL(s) failed: https://altoncanoeclub.co.uk/wc-api/Woo_Paypal_Gateway_IPN_Handler/?wpg_ipn_action=ipn If you don’t recognise this URL, you may be using a service provider that is using IPN on your behalf. Please contact your service provider with the above information. If this problem continues, IPNs may be disabled for your account.

can anyone advise on what I need to do?

The page I need help with: [log in to see the link]