UPS Manifests: "Orders were finalized. No printable manifest can be provided by carrier. Manifests are not supported by UPS"

UPS does not support and does not require paper manifests.

There is no concept for "manifest" on UPS web apps, just as Canada Post & other carriers handle them. 

They use "manifests" (they call it "end of day" report) only when you use their UPS Worldship client app.
For all other UPS integrations, the manifest is NOT required.

The UPS website states the following: https://www.ups.com/content/us/en/resources/sri/pickup3.html

By consequence, they pick up the packages without a physical manifest.

You can verify so by checking your labels. All your labels will have package symbol in the bottom right-hand corner.

If this icon is shown on the label, you do NOT need to provide a "manifest" to the driver.

You can call UPS using the phone shown above if you need more information.