Can't enable VoLTE/ Bouygues Telecom(France)

[david_descamps]

Hello,
I can't enable VoLTE.
Model Name: ROG Phone I (Z01QD / ZS600KL)
Firmware Version: 16.0420.2003.24_0
Rooted or not: Nop
Frequency of Occurrence: every time
Settings is not present in the phone parameters, and when I use the #*#4363#*# the VoLTE settings is grayed and can not be toggled.
I've double checked with my provider, the option has been activated for my line so it should be ok on their side.

[david_descamps]

Note : I already tried to "factory reset" the phone to be sure, but it did not help. I also asked my line provider to reset the option (in case it could help).

[Christine_ASUS]

Hi david.descamps
Thank you for your asking. Kindly refer to 4 main requirements below that needs to fulfill to use VoLTE function :
A. The carrier supports VoLTE
B. The model supports the carrier
C. SIM Card has VoLTE
D. Both side are using VoLTE

To activate VoLTE or VoWiFi, please refer to the check point below:
1. Which carrier are you using? Does it support VoLTE on ZS600KL?
2. Please check if you have open the VoLTE or VoWiFi
VoLTE: Settings>Network & internet>Mobile network>turn on "VoLTE">Preferred network type>2G/3G/4G
VoWiFi: Settings>Network & internet>Call>Wi-Fi calling>turn on

[david_descamps]

A) Bouygues Telecom (French carrier), I don't know if they supports the ZS600KL,
B) I don't know, but it should,
C) yes, the same SIM Card was working fine with VoLTE on my previous phone (Samsung),
D) I'm pretty sure it's ok on my carrier side, they've sent me a SMS saying that the VoLTE/VoWiFi has option has been re-enabled on my line,
Regarding point 2), I don't see those settings on my phone ... and that's kinda my main problem here.

[david_descamps]

4G data and 3G phone calls are working just fine, but I'd like to be able to keep internet connection working while being on the phone.