flashmode for xperia m2 not working

i am trying to flash TWRP - 2.8.7.0 recovery to my xperia m2 . i am successful and i can install custom ROM from TWRP recovery mode but flashmode( volume down key + power key) is not working any more, fastboot mode (volume up key + power key) is working correctly. please help me i want to install factory ROM that is provided by sony but i am stuck because of unable to turn on flashmode.
thank you

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