Can't get Closed Captioning box to display

I just upgraded to Storyline 3 and need some help with the closed captioning feature.  I have an .mp3 audio file and a separate .srt file that I created.  I have attached the .srt file however when I preview the slide and click on the closed captioning icon, I don't see a CC box on my slide.  I thought this box was supposed to show up automatically.  Am I doing something wrong?

Thanks

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