[Moto G4 Plus Questions & Answers] echo92:
From your screenshot, you didn't re-enter fastboot oem lock when it asked for the 3rd time (after the request to reflash valid images and then execute the command to lock). You may also have to open with fastboot OEM lock begin to begin the re-locking process. As far as I know, these are the key commands to lock.

fastboot oem lock begin
fastboot oem lock begin
fastboot oem lock
fastboot reboot

OEM lock begin should be executed twice (it'll prompt you to re-enter the command after warning you about data loss), then should prompt you with the same message to flash valid images before using OEM lock to formally lock your bootloader.

A few things before you proceed.

1) Ensure you have OEM unlocking enabled under Settings>Developer Options (available on the stock Motorola ROM).

2)You may not wish to re-flash your device when prompted if you are certain your device is clean and unmodified. However, your data and device is wiped anyway, and I would recommend it to ensure your firmware is not modified in any way prior to locking. Any modifications that alter your firmware signatures may be detected by the enforcing locked bootloader and prevent your device from booting whatsoever, which can be avoided by flashing a clean copy of the stock firmware before locking. If you are not sure if your device is completely stock and clean, for your device, NPJ25.93-14.7 US retail stock firmware is here: https://androidfilehost.com/?fid=817906626617945295

2a)On a related note, if the bootloader is locked and modified firmware is detected on boot (be it kernel, recovery or anything else that doesn't match the expected checksums), you would normally not be able to boot, and either would have to buy a new device or have your motherboard replaced. If you've enabled OEM unlocking as in 1), you may be able to unlock your bootloader again and get your device to boot (using the same unlock key as you've been previously furnished with).

I would thus recommend the following.

a)Back up all essential data and move it off your device. Ensure you either copy data off your SD card if you have it adopted as internal storage or have a copy of the SD card encryption key.

b)Enable OEM unlocking in Settings>Developer Options

c)Boot your device to bootloader and connect to your computer via USB.

d)Flash using the OEM locking script/commands, including flashing the whole stock firmware. Personally I would recommend flashing each command manually - copy paste each command in order to your ADB terminal, execute and wait for the [OKAY] to appear.

e)Reboot and check your device is working properly.

e1)If it is, then you can disable OEM unlocking in Developer Settings to secure your device. Bear in mind that you will not have a warranty. So if you have a device failure with a locked bootloader and OEM unlocking not enabled then a new device/motherboard repair are unfortunately the remaining options.

e2)If your device fails to boot, then unlock your bootloader and hopefully your device should boot.

Ensure you have plenty of time to do this, as with anything to do with your bootloader and system, you do not want to rush this procedure.

Good luck as always.