Did you Google that error or search here?
Preflash validation error is probably the single most common error when flashing a Moto device... Either your flashing the wrong variant image or you are using an image that is older than what you have already. The fix is simple, flash a rom that is the same or newer version of the than you have installed and is for the right model.
If that isn't possible, skip bootloader and possibly gpt.bin and continue... That simple.
Actually, I am going to have to disagree... With some caveats. If you downgrade to Lollipop from Marshmallow, absolutely no OTAs as it will hard brick. But most people can take OTAs if everything else is OK but the bootloader version. The updater will either error out or in many cases fix the problem... But there is the occasional brick depending in the "right" combination of circumstances.
So... Be safe and ignore that constant nagging or just go for it? Hmm... Your call, unfortunately no one here can guarantee success or failure.
Thanks, I think I’ll leave it, don’t want to risk bricking if it can’t be guaranteed. If it was known what caused it to brick and I could check the update wouldn’t brick mine then I would, but I’m not a risk taker haha.