Siri on IOS15 Ipad

Hello,

I really need to get to the bottom of this.

I had purchased an Ipad Mini 5 WIFI that already came with IOS15, and it

would not allow me to make VOIP calls over 3rd party apps (such as

LINE). It would give the common error described here that Siri can't

help me do that on this Ipad.

But I have an older Ipad Mini 2 WIFI with IOS 12 that does allow Siri to do it.

The problem is that The Ipad Mini 2 does not seem to respond to

completely hands-free Siri, I must press the Home button for it to

respond.

This is utterly frustrating as I bought it for a visually impaired adult that needed a replacement.

To top it off, my wife with Iphone and IOS 15 CAN use VOIP apps hands-free to call.

So my thoughts are, if its a WIFI-LTE Ipad, it may work with IOS15, but

I'm not sure if it requires the LTE SIM with an active cellular service

for Siri to see it as a "calling" device and allow VOIP?

It's really confusing what the real limiting factor is here with the facts I stated above.

1) Can anyone with Ipad Mini WIFI newer prior to IOS 15 (e.g. 12, 13,

14) confirm you can do completely free hands-free calls over a VOIP app

like LINE or Skype?

2) Can anyone with Ipad mini WIFI-LTE on IOS 15 confirm you can do a VOIP app call by voice command?

Appreciate any help.