Sorry, no knowledge about FP3+ here …
Some similar threads : FP3 installation : stuck in fastboot mode - #23 by JBdV, Device is corrupt, can't be trusted - FP3 - #9 by 7eries, Easy Installer failed - Fairphone 3 blocked on fastboot mode
Sorry, no knowledge about FP3+ here …
Some similar threads : FP3 installation : stuck in fastboot mode - #23 by JBdV, Device is corrupt, can't be trusted - FP3 - #9 by 7eries, Easy Installer failed - Fairphone 3 blocked on fastboot mode