Can't restore stock firmware with fastboot

[jextrevor]

I flashed a custom Oreo 8.1 ROM onto my Moto G4 Plus, and decided to go back to the stock firmware.

However, when attempting to restore the firmware with fastboot, several of the commands fail:

writing 'system'...
(bootloader) Security version downgrade

(bootloader) Image s failed validation

(bootloader) Invalid signed image
(bootloader) Preflash validation failed
FAILED (remote failure)

How can I restore the stock firmware? Is there another way, other than through fastboot?
Any help is greatly appreciated.

I installed the custom Oreo rom found here: https://forum.xda-developers.com/moto-g4-plus/development/rom-android-source-project-t3716697
I downloaded the firmware found here: https://forum.xda-developers.com/showpost.php?p=74467073&postcount=413
I followed the instructions found here: https://forum.xda-developers.com/moto-g4-plus/how-to/stock-rom-npjs25-93-14-4-march-1-t3608138

 

[jextrevor]

I may have figured it out - looks like I was trying to flash the non-US firmware instead of the US firmware. I'll let y'all know if I get it figured out or not.

 

[jextrevor]

Never mind, it's all good!! A lesson to others to check the build numbers and software channels before flashing.