PayPal is transitioning to ship station for labels, I believe it should be completed by January. You still pay via PayPal, but the labels are through ship station and not USPS. I would assume USPS is still the carrier for all packages.

I've had some issues with them during the transition period. They have "misplaced" payments for some of my labels and USPS claims I owe underpaid postage. PayPal has receipts for the payments thankfully. Hoping it's just a hiccup and gets resolved quickly as it's prohibited me from printing further labels.