Label printing APIs are down for PayPal, Pitney Bowes, stamps.com, Amazon.com Seller Central, and USPS' own Clin-n-Ship webapp
Site:
From PayPal:
We are currently unable to contact the US Postal Service. Please try again later.
From USPS cns webapp (Clin-n-Ship):
This service is currently unavailable
This service is temporarily unavailable. We apologize for any inconvenience this might cause.