Enter the Unlock Code: Once prompted, carefully enter the network unlock code you received. If you don't have an unlock code, you would need to obtain one from the carrier where the device was purchased. (as an example: if it was purchased from Tracfone ...
From the Root post: "If on AT&T you need a 1st Gen Moto X Developer Edition or a Moto X 2nd Gen Pure Edition orGoogle Play Editiondevice (Moto G - GSM only) device. This restriction also extends to AIO Wireless (AT&T) and Tracfone devices." ...