In order to unlock the device using the Mi Unlock Tool, the device need to be bind to the Mi Account in order to get the permission and to successfully unlock the device, this has been the usual protocol in all other Xiaomi phones.
As far as we know, Redmi K30 4G (phoenix) unlocks well, but Poco X2 (pheonixin) cannot be unlocked as of now because of the error.
Steps to reproduce:
1.Go to Settings -> About Phone and tap the MIUI version multiple times to unlock Developer Options.
2. Go to Settings -> Additional Settings -> Developer Options -> Mi Unlock Status
3. Here you can see an option at the bottom to Add account and device, if you tap it, you'll meet an error which says: "Couldn't add. Error code:86023"
Device cannot be unlocked until the account and device gets binded.