VoLTE does not work with BSNL on trixie

With BSNL netowrk, when a call comes, it always switch to 2G. When sending the SMS to activate as per instructions found online, it says VoLTE is active already.

I cannot check the VoLTE status after installing bm818-tool (https://source.puri.sm/Librem5/bm818-tools ci generated deb)

bm818-volte-check
/usr/bin/bm818-volte-check: line 7: chat: command not found
BMRAT state not active

Update: since VoLTE is not working, to make calls we have to switch to 2G only mode (incoming calls switch to 2G automatically).

Update: VoLTE works well with Vi network on Librem 5 and BSNL network VoLTE works well with FLX1 (which uses a different stack for modem management ofono).