This is the “Fairphone Unlock page” Bootloader Unlocking Code for Fairphone - Fairphone … it contains full instructions. I am not certain, but I thought that this was a one time event. I don’t think you want to be doing this with easy installer, I think that you need to carefully sort out –
- has it been done already?
- or is it still to do? (I do not believe this is a job for easy installer [1])
While the following three are not perhaps fully discrete, we have to be careful about using the right term for each.
- The Fairphone unlock process.
- OEM unlocking. (Notice how the Fairphone Unlock depends on Developer options → Enable OEM unlocking)
- Locking and unlocking the Bootloader.
I didn’t realise that the tutorial I already linked, leaves you to sort out the The Fairphone unlock process yourself. However it does cover the other 2 locks fully.
Maybe you are drawing the wrong conclusions from Easy Installer failure. You could look for logs.
This is the Official install page Install /e/OS on a Fairphone FP3/3+ - “FP3”.
[1]