Sounds seem to be working on my machine, so could you provide a few more details such as:
What operating system are you using?
What Stream Deck software version do you have?
What version of TomatoTimer are you using? This can be found by right clicking on the Timer activity in the list of all activities in the Stream Deck configuration UI
Do other Stream Deck sounds work? The built-in Play Audio activity can be used to test this
Does the sound not play correctly when clicking the "click to play" preview button, when the time expires, or both?
Neither default sounds nor custom sounds work