I am not sure about Kiss toppers, but the Stern toppers I have bought have their own node board, node 12. If the game was communicating with the topper properly node 12 would be showing up in your diagnostics.
Why it isn't being detected? Who knows. If it were me I would take it apart and take a look to see if there are any obvious loose/disconnected things. If there is a node board inside, it might have LEDs that would show if it is getting power or not.
If nothing obvious, my next step would be to contact Stern support.