PayPal has scheduled a system-wide maintenance window of 25 minutes on May 26 (or May 27 depending on your timezone). You can find more info here:May 26th Maintenance

Excerpt From Paypal website:
REMINDER: This is a reminder that we will be performing system maintenance to improve the reliability and quality of our services starting May 26, 11:00 PM PDT (May 27, 6:00 AM GMT). Please note that the corrected maintenance end time is May 27, 1:00 AM PDT (May 27, 8:00 AM GMT).


During this maintenance window we are expecting to have **PLANNED DOWNTIME** of approximately 25 min which is expected to take place sometime between May 26, 11:00 PM PDT (May 27, 6:00 AM GMT) and May 26, 11:30 PM PDT (May 27, 6:30 AM GMT). As a result, merchants will not be able to process transactions during this time.


During the planned downtime window, the PayPal website (https://www.paypal.com) and PayPal APIs (including Express Checkout) will experience a service interruption and buyers attempting to make payments will be unable to do so. We expect that the majority of API requests will not complete and will fail with error 10001 (Internal Error) or time out. Attempts to log in to www.paypal.com will result in an error message.

PayPal System Status Page:
You can always check PayPal's system status and scheduled maintenance at:
https://www.x.com/community/ppx/system_status/mts_updates