Instant Payment Notification failed and Responding web hooks FAILING

[bb9009]

We get the issus as belows, I dont know if the PHP versions problems or the plugins problem...
Instant Payment Notification failed!2Checkout system failed to receive a valid reply to the IPN notification sent for the following orders:

Our system detected that you have slow responding web hooks.
Over the past 3 hours the URL https://xxxx/?wc-api=2checkout_ipn_inline is FAILING to respond to our calls.
This can create IPN/LCN delivery delays.