Just to make sure … You recently posted that you bought a phone and wanted to make use of the current earphone promotion … this would mean you bought a Fairphone 3.
This topic here is about the Fairphone 2. If you are sure you are doing this to a Fairphone 2 
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Please follow steps 1. to 4. of this guide to install TWRP and wipe the phone, just don’t reboot at the end like the guide suggests, but from TWRP’s main menu do Advanced - ADB Sideload and try to sideload the /e/ install file again.