What if I miss a day of studies?
If you have studied three days in a row, then there is a free "pause" option that basically deletes one day from your study timeline and appends +1 day to your fluency goal date. This is called the streak saver, and it can be toggled on or off from your study settings page.
This does not affect your reviews. The streak saver is the "skip a day without messing up my learning streak" feature.