Re-locking Pixel4 Bootloader Issue

[Sheikh Sam]

Hi! I am flashing AOSP on a pixel 4 and pixel 4a device, but once after flashing the AOSP into the device, it works fine until the device is in flashing unlock state but when I tried to re-lock the bootloader, the pre-installed AOSP would not load and the device shows error "Invalid OS" failed to load OS.
Can you guide me on how to re-lock after flashing especially in pixel 4 and 4a devices?

Attached below is the issue I'm facing right now
Waiting for your response.
Thank You