Always ensure you use a loader file specifically signed for OPPO devices. Generic loaders for other Snapdragon 665 phones (like Xiaomi or Realme) may fail due to different security signatures.
This implies that the loader file you are using is not authorized or does not match the exact hardware revision of your Snapdragon 665 chip. Ensure you download an updated, verified "unlocked" or "patched" firehose file tailored specifically for OPPO's secure boot parameters. oppo a5 2020 loader file
Carefully remove the back panel and internal shield of the device to expose the motherboard. Always ensure you use a loader file specifically
If the tool allows a custom file, browse your storage and upload your extracted prog_emmc_firehose_sm6125_oppo.mbn loader file. oppo a5 2020 loader file