i had the same problem i tried to instal gcam but i was usin a costom rom and my phone got bricked, my only hope was EDL mode but i did know how to do it, i just went to the service xiaomi and the fixed i recomend to you do the same, go to xiaomi ...
you can try tu put in edl mode with command "fastboot oem edl" if screen become black and led is blinking you are in edl and you need qdloader driver, then try to flash with miflash.
this is the last hope then you must use test point
take a lo...
Thanks a lot I could flash the zip via twrp and I been testing the rom all day and it's working fine if I find some bug I'll let you know :D