'Bloon Tower Defence 4 - Sandbox Mode' won't let me add bloons for me to pop

I have been playing Bloon Tower Defence 4 for a while (please don't judge me playing old games), and I just couldn't wait until I get to Carrer Rank 26 when I can play in Sandbox Mode. I've got to Sandbox Mode now, but when I try clicking on the buttons at the top of the screen, nothing happens - no bloons come onto the screen. If it helps I am using the browser 'Safari' on an Apple Macintosh Macbook Air, for whom it may concern.

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