C31 Doorbell - Wired connection issues

I am trying to set up my C31 with a wired connection using the wires from my previous doorbell. As my old transformer was only 8v I have installed a new transformer which is delivering 16V at the bell. However when I use the Switch Mode feature in the app I am getting a message that says the doorbell wires are not working. In the app I can that there is power as the battery is being charged.

Can anyone suggest anything else that I can do to resolve this?

I had to upgrade to 24v ac. I jumped off the one that powers my furnace 24v ac bus bar