How do I prevent Keynote text boxes auto fitting the text to the box?

If there's overflowing text in a text box in Keynote 9 for Mac, how do I prevent Keynote from scaling down the size of the text?

I need the text in my presentation slides to be the same size. If there is too much text, I want to see the + at the bottom of the text box, not have Keynote shrink it. And there are situations that I can't increase the size of the text box - it is better for me to move overflowing text to the next slide.

Thanks for any help!