[Q] Any way to apply OTA update with unlocked bootloader and custom recovery?

My son's XT1031, which has an unlocked bootloader and TWRP recovery, has been continuously requesting to install an OTA update (221.31.4). I tried to install the update zip file I found in the /cache directory but it fails to install. Does anybody know how to install the OTA with a custom recovery? The phone is stock Android 5.1 (221.21.56) otherwise.

Thanks in advance.

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