This is the most reliable method for the SM4250 chipset.
Vivo does not publicly host firmware files on their official website. Instead, they are distributed through authorized service centers. However, reliable third-party repositories have archived the 2021 builds. vivo y12i firmware 2021 upd
| Error Message | Cause | Solution |
| :--- | :--- | :--- |
| "Sahara Fail: qsaharaserver fail" | Wrong driver or USB cable | Reinstall Qualcomm 9008 driver. Use USB 2.0 port. |
| "Firehose – Invalid image type" | Wrong programmer file | You used a 660/845 programmer. Download the SM4250 specific elf file. |
| "Only nop and sig tag can be received" | Anti-rollback protection | Your phone has a newer bootloader. You cannot downgrade to 2021 firmware. |
| "Userdata image too large" | Partition mismatch | Use the rawprogram0.xml from the EXACT 2021 update package. | This is the most reliable method for the SM4250 chipset