Fix Realme C21 RMX3201 “Download Not Completed” Error | Oppo_Custom.bin Solution

If you’re flashing firmware on your Realme C21 RMX3201 using SP Flash Tool or Realme Flash Tool and get the dreaded “Download Not Completed” error, don’t panic. This issue is very common on MTK (MediaTek) devices, especially when using modified or incorrect firmware builds containing Oppo_Custom.bin.

In this guide, we’ll explain why this error occurs, how to fix it safely, and how to flash your Realme C21 successfully using official firmware from MobiFirms.com.

Why “Download Not Completed” Happens on Realme C21

The main cause of this error is a mismatch between the Oppo_Custom.bin file and your phone’s partition layout. Realme and Oppo devices often share firmware structures, but small differences in region or model variant can lead to errors during the flashing process.

Common causes include:

• Corrupted or incomplete firmware download
• Wrong region firmware (India, EU, or Global)
• Incorrect Oppo_Custom.bin file version
• Outdated or modified SP Flash Tool
• Secure Boot or DA (Download Agent) mismatch

Step-by-Step Fix for “Download Not Completed” Error

1. Use Official Firmware

• Download the official Realme C21 RMX3201 firmware from MobiFirms.com.
• Make sure the firmware version matches your device’s region and build number.
• Verify that the Oppo_Custom.bin file size is correct (usually 30–80MB).

2. Extract and Replace Oppo_Custom.bin (if corrupted)

• Unzip your firmware package.
• Locate the Oppo_Custom.bin file.
• If the error persists, download a fixed Oppo_Custom.bin from MobiFirms’ Fixed Firmware section.
• Replace the existing one in the firmware folder.

3. Use Correct Flash Tool + DA File

• For MTK Realme devices, use SP Flash Tool v5.2124 or higher.
• Load the auth_sv5.auth and MTK_AllInOne_DA.bin files provided in the package.
• Choose Download Only mode (not Format + Download).

4. Check USB Drivers & Connection

• Install MediaTek USB VCOM Drivers properly.
• Use a direct USB 2.0 port (avoid hubs).
• Connect the device in power-off mode while pressing the Volume Up button.

5. Try a Fixed Firmware Package

If the error still appears, use MobiFirms’ “Fixed Firmware” tested version for RMX3201. These builds include a patched Oppo_Custom.bin and verified scatter file, ensuring a successful flash.

Pro Tip

Always verify your device’s secure boot status before flashing. Some Realme C21 units have a locked boot chain, which rejects custom partitions like Oppo_Custom.bin. In such cases, use Authorized DA and Auth files or perform flashing via Online Authorized Tool (e.g., Hydra, UMT, or EFT Pro).

Final Words

The “Download Not Completed” error on Realme C21 RMX3201 can be easily fixed by using the right firmware and replacing the Oppo_Custom.bin file.
👉 Download 100% tested Realme C21 firmware and fixed files now on MobiFirms.com to restore your phone without risk.