Hey there, Snyderk08! The factory unlocked iPhone 8 Plus is compatible with us. However, if you bought the phone directly from Sprint, it is not compatible. Since we run under the Sprint network, the methods of activation for Sprint phones are not the same as for factory unlocked devices (or unlocked devices from non-Sprint carriers). You can find a list with the compatible unlocked phones through this link http://boost.co/2gB0A9C. The list of compatible Sprint devices can be found here http://boost.co/1URk98c.
Bear in mind that even if Sprint unlocks your device, it won't be compatible through the Bring your own device program until it is shown on the list of compatible Sprint phones (this is if you purchased the phone directly from Sprint).