Signature verification failed & failed to find update binary

I’ve been following the Unified Installation Guide for my Fairphone 4 and I get stuck on step 8.
I do the “adb sideload” command and after about a second, my phone shows the following message:

Finding update package…
Verfying update package…
E:footer is wrong
Update package verification took 0.3 s (result 1).
E:Signature verification failed
E:error: 21

On my phone, after being asked “Signature verification failed Install anyway” I now select ‘Yes’
I get the following output:

Installing update…
E:Failed to find update binary META-INF/com/google/android/update-binary

I feel like I’m missing something but I don’t know what, can anyone help me in the right direction?


Indeed, the FP4 manual upgrade guide is wrong.

It’s not possible to “adb sideload” an “IMG” file.

See open tread here:

Any idea how to proceed instead? The thread you linked to shows a lot of issues, but not really any solutions.

I do not have Fairphone experience but what the link points to is that only the dev builds are flashed by adb sideload while the bigger stable builds are flashed by fastboot. This second method is described here Install /e/OS on a Fairphone FP4 - “FP4”.

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Thanks for your help. That seems to only from from Linux or Windows, so it’s not the right solution for me. Any other ideas?

If you wanted to continue as before you would simply need to select a dev build (which you will find linked from the install page above).

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I have a FP3 and got the same problem when updating from Android 9 (dev) to Android 11. I solved it by first going through the installation of the FP3 stock ROM, as described here (steps 1-4), and then

  1. going again into the fastboot mode (first time was to flash the Fairphone Android 11 stock ROM; with Power+VolDown)
  2. again unlocking the phone with fastboot flashing unlock. After that in reboots automatically (I let it boot into the OS).
  3. rebooting into fastboot
  4. unzip (the one I used) and change into the extracted directory.
  5. and finally execute the

After that I could simply reboot into my shiny /e/ Android 11.

This is basically the same procedure as to install the stock ROM.

That doesn’t seem to work from my Mac (M1).

Any suggestions?