Hey there, I have been trying to relock the bootloader on my FP6 unsuccessfully for a while now and the message “Your device is corrupt, it can’t be trusted and will not boot” you received while you were trying to relock the bootloader is an indication that the FRP was triggered. I got mine triggered when I attempted to flash iodeOS 7.4 on a device running /e/OS. waiting a month and flashing iodeOS 7.5 on it did not solve the problem either. So using an LLM, I ran a troubleshooting session and received following diagnosis and recommendation:
Based on your details, this is very likely an Android rollback protection / security patch level problem, not a bad flash.
The key clues are:
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fastboot flashing lock fails immediately
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the phone returns to fastboot with “device is corrupt”
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you can still unlock and boot iodéOS again
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you came from /e/OS
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FP6 has strict rollback protection
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this exact pattern has already happened to other FP6 users on iodéOS and /e/OS (Fairphone Support)
What is probably happening:
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Your previous /e/OS installation had a newer rollback index / security patch level than the iodéOS build you flashed.
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When the bootloader is unlocked, Android allows booting anyway.
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The moment you try to relock, Android Verified Boot (AVB) enforces rollback protection and rejects the installed system as “corrupt”.
The important thing is:
you are NOT hard-bricked because get_unlock_ability: 1 still works.
The most likely fix
You need to first install a firmware/base system with a security patch level equal to or newer than the one your phone previously saw.
Because you do not remember the /e/OS patch level, the safest approach is:
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Flash the newest official Fairphone OS available for FP6
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Boot it once completely
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Update it fully through OTA
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Unlock again
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Reflash the newest iodéOS build
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Then relock
This usually resets the rollback mismatch chain safely.
Recommended recovery sequence
Step 1 — Return to latest stock Fairphone OS
Download the newest FP6 factory image from Fairphone Support
Then flash it completely.
VERY important:
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do NOT skip any partitions
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do NOT keep userdata
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let the official flashing script handle both slots
Step 2 — Fully boot stock OS
After flashing:
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boot into Android normally
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complete setup
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connect to Wi-Fi
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install ALL available OTA updates
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reboot until no more updates remain
You want the newest possible:
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Android security patch
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vendor patch
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bootloader firmware
This matters because FP6 rollback protection appears tied to vendor SPL too. (/e/OS community)
Step 3 — Verify patch level
In Android:
Settings → About phone
Check:
- Android security update
Make note of it.
Step 4 — Unlock again
Enable:
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OEM unlocking
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USB debugging
Then:
adb reboot bootloader
fastboot flashing unlock
fastboot flashing unlock_critical
Step 5 — Reflash iodéOS
Use your:
iode-7.5-20260506-FP6-fastboot
This is newer than the early problematic FP6 iodé builds. (iodé community)
Step 6 — BEFORE locking
Boot iodéOS fully once.
Then check:
adb shell getprop ro.build.version.security_patch
If it is older than the stock Fairphone patch you installed in Step 2, DO NOT LOCK.
Step 7 — Lock correctly
Then do:
adb reboot bootloader
fastboot flashing lock_critical
IMPORTANT:
When the phone reboots:
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immediately hold Volume Down
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return to fastboot
Then:
fastboot flashing lock
This order matters on FP6. (Fairphone Support)
One more important thing
Your output shows:
slot-successful:b:no
slot-successful:a:yes
That is not automatically bad, but it suggests slot B may never have been fully booted after flashing.
If the problem persists after the stock-update procedure, the next thing I would investigate is whether the iodé installer only populated slot A correctly and left slot B inconsistent for AVB verification during relock.
If you get to that point, I can walk you through checking:
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active/inactive slot contents
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AVB metadata
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vbmeta signatures
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rollback indexes
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slot synchronization
without risking a hard brick.
*At this point, though, the rollback/SPL mismatch explanation is by far the most probable cause.
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On my FP6 I have paused at Step 4 in the above Recovery Sequence because FairphoneOS latest build for FP6 (FP6.QREL.16.61.0) has an Android Security Update dated April 5, 2026 which is newer than the April 1, 2026 Android Security Update for iodeOS 7.5.
So, I will wait another month and give it another try again once more with iodeOS 7.6. If that attempt triggers the FRP again then I will look to install some other OS on my FP6 frankly as my current phone is barely holding charge to get me a through an entire day. Hope this helps as in the above proposed solution by @rik, he is not expressly asking you to go back to Fairphone OS to unroll the FRP back. If you remain on iodeOS after the FRP is trigerred, you may not be able lock the bootloader even with a newer version of iodeOS, at least that was my experience…*
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