Vbmeta error when installing twrp

Executing ‘fastboot flash recovery twrp-3.5.1_9-0-condor.img’ produces:

WARNING: Flashing vbmeta image is required prior to flashing recovery image.

I’ve yet to unlock the phone and assume that’s unnecessary at this stage.

What am I doing wrong?

Regain your privacy! Adopt /e/ the unGoogled mobile OS and online servicesphone

I’ll try to unlock the bootloader first.
Please see here : https://wiki.lineageos.org/devices/condor/install#unlocking-the-bootloader

I thought I did. My steps were:

adb devices

adb reboot bootloader

fastboot devices

fastboot oem unlock

I then receive the message ‘Please re-run this command to continue.’ After doing so my phone displays a screen with START and up/down arrows. However, the last two lines display ‘oem_locked’ and ‘Transfer Mode: USB Connected.’ I’m not presented with a screen asking me to confirm the request by selecting ‘yes.’ The phone screen is unresponsive.

However, I’m confused between unlocking the bootloader and unlocking the phone. Are they different?

The document ‘Enable USB Debugging and OEM Unlock’ instructs me to enter ‘fastboot oem unlock.’ However, 'Install /e/ minimal on a Motorola Moto E - “condor” tells me to enter ‘fastboot oem get_unlock_data.’

Unfortunately, ‘fastboot oem get_unlock_data’ gives me the vbmeta message I originally referenced.