1. Go to Settings->SIM cards and mobile networks->choose appropriate primary SIM if You have two SIM's and edit APN's from this SIM (use guide from the beginning of this post to do this, just throw out "mms". MMS service has it's own separate APN)
2. Install com.google.android.ims.apk (download this apk from apkmirror).
3. Install com.activitymanager.apk
4. Run activitymanager app, find com.xiaomi.mbnloader and choose Your carrier.
5. Again in activirymanager app find com.qualcom.qti.ims.ImsSettings and enter Your SIM international number.
6. After this, best will be to reboot and after successful reboot enter dial codes from beginning of this guide to activate (in fact this disables checking from provider side) VoLTE and VoWiFi, after this best will be to again reboot your phone.
I hope that this answers will help You?!
For God sake please use different color to emphasize Your question second time, this yellowish is horrible and unreadable!!!
Suddenly today... I didn't do anything [emoji23][emoji23][emoji23]Yep!
All without root access on MIUI 10!
But You have a right, let's just say that this "guide" is old and obsolete now.
Unfortunately new MIUI comes with new issues and obstacles but usually keeps errors and miss features from previous ROM iterations.
Beauty of Xiaomi's MIUI ecosystem.
I have a Mi 9 global version running the latest stable global Room. I'm trying to turn VOLTE on, but I'm nota being sucessfully.
I've tried enable It via MCC code (*#*#4636#*#*) but It doesnt work. The option to enable VOLTE os greyed out.
How can I enable It? My old s7 suport VOLTE with the same sim card.
Are you on the EEA ROM? Xiaomi is having problems with bugs in MIUI builds that are supposed to be stable but the EEA ROM for the MI 9 seems to be especially snake bitten.
If you are on the EEA ROM I would seriously consider switching to the Global instead which doesn't seem to be experiencing issues as serious as those on EEA.