While possible (fastboot oem lock), relocking a bootloader on a device that has been modified (custom ROM, modified system partition) will brick the device. The only safe way to relock is to restore the exact factory firmware image first.
When using the top official unlock site, you might see: motorola bootloader unlock site official top
Here is the official text for finding Motorola’s official bootloader unlock site: While possible ( fastboot oem lock ), relocking
"To unlock the bootloader on your Motorola device, visit the official Motorola Bootloader Unlock portal. Go to: motorola-global-portal.custhelp.com/app/standalone/bootloader/unlock-your-device" motorola bootloader unlock site official top
For clarity and safety, always ensure you are on the official Motorola support domain (motorola-global-portal.custhelp.com) before proceeding.