Missing toggle on and off button on the ipad

Im not sure what you mean by Toggle. The two apps are both separate. They both use a Apple ID for some features, but are not really linked, just similar services. You can start a FaceTime call in messages by Pressing Details inside of a conversation and then pressing the video icon, im not aware of one in the FaceTime App, and I dont know of a toggle between the two, as Video calls and Text messages are both separate features

Where are you looking for a toggle switch? Do you mean in the settings?

Do you mean the Video Icon doesnt appear in the contact? Have you checked that FaceTime hasnt deactivated itself??

See if its enabled in Settings > FaceTime. If it is, try turning off and back on Again. Will then reactivate.

Also the icon doesn't appear unless the person you are speaking to has FaceTime enabled, so check that they haven't disabled their FaceTime. That might explain why the icon doesn't appear.

Do you have a stable internet connection?? Apple Status isnt showing FaceTime as down so that should be OK. Could try Turning off FaceTime, restarting the phone and then turning back on, see if it then lets you activate.

Apple has a Article on this which walks though timescales and what to do and who to contact if it still doesnt work:

https://support.apple.com/en-us/HT201422

If not might need to contact Apple and Check your Apple ID. Hopefully that helps?