Update: We managed to re-send the last 24 hours of transactions from PayPal successfully and the shop should now be functional again. A few transactions remain but we will sort them out at the latest tomorrow.
We are currently experiencing communication issues with PayPal. We are investigating the reasons but be prepared that payments using PayPal may take quite a while before they are going through since we will have to deal with them manually unless we manage to fix the reason behind the issue.