Not all OPPO phones can be unlocked. Carrier-locked variants (Verizon, AT&T, Vodafone) disable this entirely. Chinese ROM devices have different rules.

: Try booting your phone into "Fastbootd" mode (which looks similar to recovery mode) by using the command adb reboot fastboot . Once there, you may be able to execute standard fastboot flashing commands that were blocked in the primary bootloader.

This article dives deep into what this error means, why OPPO enforces it, the technical mechanics behind the "serial mismatch," and—most importantly—the real solutions (and the harsh truths) about bypassing it.