In case you received a letter from PayPal about their transition to SHA256 cert signing and G2 to G5 certificate authority swap, you don't need to worry.
Nothing needs to be done on your side.
(There might be a slight (< 0.1%) chance you're using a very special IPN module. In that case, payments will be received by PayPal, but won't be reflected in your shop software. In this rare case, contact us.)