Dial *#06# . Write down the two IMEI numbers. They should match the sticker under the SIM tray. If they show "Unknown" or "NULL," the flash erased your NVRAM. You will need to restore your IMEI via Maui META Tool (advanced topic).
This article details exactly what refurbished firmware is in the context of the Oppo A78, the dangers of using it, how to identify it, and how to restore your device to the official factory state. oppo a78 refurbished firmware
🔁 if provided by the source to avoid corruption. Dial *#06#