Cannot connect with tested switcher.

Cerevo has officially confirmed some switchers are compatible with FlexTally.
See this page to find the list of tested switchers.

However you may not connect with  a switcher on the list when your firmware is not up-to-date. Please check if your firmware is up-to-date when you cannot connect with your switcher.  If not, update your firmware and try again to connect with the switcher.
See this page to find steps to update firmware.