well i have this problem too earlier on. i was using global beta rom miui10 and decided to flash to china dev rom miui10 for a change. so after flashing it asked me to sign in my mi account, i typed the correct password yet it doesnt log in! so i changed my mi account password using PC and tried to sign in again still no hope. i flashed back miui 9 stable and still its asking me to sign in.. i sign in and it tells me invalid USER ID! after that it gave me a series of number ask me to give to customer care for them to unlock my phone.. plus they need proof of purchase.. i bought my mi6 from a local seller... and now i guess im stuck with CUSTOM ROMS only~~ anyone ever fix or bypass this pls help me out OR can i flash and use this xiaomi EU rom without any problem?