S8 don't support DUAL VoLTE and check this out

[aakarsh9]

This is by Official Samsung Electronics operators

[uk29]

so dey hav cleared s8 nd note 8 won't get dual volte

[theKeshavKr]

Yeah!

[Shubhammore]

A8 STAR DUAL VOLTE UPDATE GIVE SAMSUNG GALAXY A8 STAR DUAL VOLTE UPDATE

[Bhava003]

Also J6+ Dual VoLte Support but S8 & Note8 (Flagships) not support Dual VoLte.

[RP5054]

Dual volte is supported by processor. At the time of s8 and note8 there was no such thing like Dual Volte. Dual volte become famous in 2018. Most of the 2018 processors came with dual volte support.
So your phones processor doesn't support it.

[RohanGhag]

it is not about processor it is About the Radios And Modems used inside it. For ex:-galaxy m10 has exynos 7870 yet it supports dual volte

[RP5054]

Yeah it is same thing. It is an add on to processor. You cannot modify motherboard of s8 and note 8 now. That's what i'm saying.

[divyansh54]

for dual volte a hardware is needed

[arv7801]

why do you need dual volte ? I have dual volte support on my s9 & i don't even use it on any of my sim..