ZE551ML: flash firmware

Asus ZenFone 2

1. Unlock boot loader.
   Unlock Device App you can find at https://www.asus.com here in Utilities:
   Direct link.
2. Download lastest firmware… you can find it at https://www.asus.com here in Firmware (select “for WW SKU only*”)
   Also, direct link can be curled:

URL='https://www.asus.com/us/support/Download/39/1/0/13/Lk0Sg1Ulh0Ph49Hl/32/'  
curl -s $URL| grep -o "\"http://dlcdnet.asus.com/pub/ASUS/ZenFone/ZE551ML/UL-Z00A-WW.*.zip\""  
"http://dlcdnet.asus.com/pub/ASUS/ZenFone/ZE551ML/UL-Z00A-WW-2.20.40.174-user.zip"  

3. TWRP
   u can found here https://dl.twrp.me/Z00A/ (twrp-3.0.0-0-Z00A.img 15.3M )

4. adb sideload