: Wipe specific sections of your phone's storage or change file systems. Phase 1: Essential Prerequisites

You should see your device serial number.

Open the folder on your computer where you installed the ADB and Fastboot tools.

This error confirms the bootloader is locked. Without an official unlock code or a paid unlocking service/tool, standard flashing is impossible.

Vivo devices have locked bootloaders, which prevent custom recovery installations. You must unlock it via fastboot.

Once you have a TWRP .img file and an unlocked bootloader, follow these steps.

Download the specific standard recovery .img file matching your exact Y71 variant.