Some guesswork sparked by this bit:
If you never logged in on this backup FP3+ with your own Google account, then it is probably still tied to the previous owner of your backup FP3+ who apparently did not unregister her or his Google account before selling the FP3+ to you. Most likely that Google account holder is the only one who can unblock it then.
Three ideas following from that:
- The previous owner of your backup FP3+ unblocks it for you. From my experience, this usually does not materialize, but it is up to you if you want to contact the seller again and ask.
- Check if the current backup FP3+ is on the latest version of Fairphone OS. Fairphone introduced a simplified bootloader unlocking on the FP3 with the mid-March (2026) Software Update: FP3.6.A.040.2 📲 As I am not using Fairphone OS myself, I do not know exactly what changed to bootloader unlocking, so I cannot know if this would help you overcoming the Google account blockade on your backup FP3+. But it cannot hurt if you check the Fairphone OS version on it and update it to the most recent version (if it is on an older one).
- Alternatively: Consider if you are willing to switch the “roles” of your two FP3s – make your current primary FP3 the backup one and the backup one the primary one. Your current primary FP3 should allow the change to Murena’s /e/OS if you unregister your own Google account from it.
If any of that is successful, my own experience with switching a Fairphone OS FP3 to /e/OS using Murena’s web installer at /e/OS Installer last year was very good.
For others reading along, I got contacted in private and that message included some more info (the backup phone is a second hand one). The discussion should continue here now.