What does "The Shippers shipper number cannot be used for the shipment" mean?

There are 3 potential causes to this UPS error

  1. Confirm that the 'from address' matches the address you have set in your UPS account.
  2. Make sure that your Shipper Number is connected to your ups.com account. (See steps here)
  3. Log into your UPS account, or call your UPS rep and check that your account has not been suspended.