@bixsyafiqsaini , You can also check if your username and password that you keyed in are correct and valid. Contact 100 or Live Chat unifi to check the details.
Mine also LG webOS TV. I just called 100 because I was having the exact same problem just like you. The staff said the ID and password that I have cannot be used on the app. It only can be used on phone. If you want to watch unifytv on LG, you still need to have tvbox.
maybe ur id only use for unifi@play tv, can't use for unifi tv. that why you can't log in ur id on ur LG TV. you need to upgrade unifi tv pakej. unifi tv have aneka pack, ruby pack, varnam pack and ultimate pack. you just addons RM30 on ur bill.
if you want upgrade just call 100 for tm customer service. 1-5 day can activated ur id for unifi tv pack.