I have tried today thru my mac pc. but failed to do. Not find a single video about this tutorials so far. Briefing the step by step what I did
1) Reboot by pressing power key + volume up key (2) fastboot screen appears where fastboot is in "red" mark & Device Locked is in red mark too (3) plug the USB cable to PC (4) I have open the terminal & unzip the WW-ZS620KL-10.03.4.52-BSP-user_52-release.zip (5) gone to the folder & click on the update_image_for_mac (6) on my phone nothing is appeared & on pc terminal window it gets scrolled & finally it says download fail...download fail...(7) I have tried 5-6 times but it remain same. Tried to check fastboot method thru any other forum or social media like youtube but surprise to see there is not a single post of fastboot method for zenfone 5z. all other cheap zenfones tutorials are there but for this flagship, no tutorial. (7) I have filled up the google form & given the link on the screen recorded video. Expect you should give step by step tutorials with screen shot of each & every steps. For your information, I have enabled developer option to enable USB debugging.
Hope I will get help. If not nothing worries.
