If you need to stop in the middle of a mani, long press the center Paint button until all buttons flash, and then let go.  Your app will also notify you that you’ve stopped your mani and prompt you to tell us why.  Once your Nimble goes back to Capsule Ready, it’s ready to be powered down.

Caution:  if you stop a mani, you will have to start from the beginning again!  Your Nimble will not paint additional coats on an already-painted finger.