This article applies to merchants who have connected Nexternal directly to UPS, and are not connected through EasyPost. If you are directly connected, you will see this at Settings / Compatible Software / Online Shipping Tools:
Once you have confirmed that you are directly integrated, if you attempt to generate a UPS label and get this error: "Invalid Authentication Information", here's how to fix it:
First, read the NOTE below. Then navigate to Settings / Edit Compatible Software / Online Shipping Tools / UPS Developer Kit and choose 'Manage'. On the next page you can delete your registered UPS Shipper Number. You are then able to add it again by selecting 'Register' in that same place. The UPS account and UPS shipping should start working again.
NOTE, BEFORE YOU DO THIS - if your shipping rate tables are already established, be sure to keep a copy of your shipping settings, as they may be affected by this deletion and re-registration. If you are using real time rates for example, you may need to go back to the shipping tables after re-registration of the UPS Kit, and check all the RTR (real time rate) boxes again.