Question about documentation!

I work for a home healthcare agency. We require our nurses to fill out a time sheet. Not sure if this is required everywhere, but it's got clinical information to fill out as well as time in and out for the shift.

I was told by my boss when I started processing payroll that of a nurse/CNA does not submit documentation, that they won't be paid until they do. The payroll specialist before this boss came used to have people who didn't submit documentation on time email or call with their times and just pay them off of their word.

Now this boss has left, and upper management is saying that we can't "legally" not pay them if we "know in good faith that they worked."

does anyone know if this is true? We even have a mobile app for submission now. If a nurse doesn't submit documentation either by mailing to the office or PROPERLY submitting an image through the app, are we required to pay them by law? If not, where is the line drawn? How are we supposed to know "in good faith" that they worked if we don't have documentation to prove it??