UPDATE: I should have read the instructions! You're not supposed to click and drag things around directly. Use arrow keys to move the cursor, and x/spacebar to click. Move the window by using these controls to click the diamond and then move the arrow keys.
ORIGINAL COMMENT:
How exciting! Bought and downloaded for Mac. On 10.14.6, the window opens in the middle of the screen, plays sfx and seems to be running, but input isn't captured. I can't click on the clickbox! Also, when I drag the window, it snaps back to the middle of the screen immediately, which seems weird. Happy to test new versions or troubleshoot further. Thanks!