The paper cassette may be out of paper or not properly installed.
If it is empty, load a new stack of paper into the paper cassette.
If there is paper in the paper cassette, make sure it is straight.
If the paper is curled, straighten it before printing. Sometimes it is helpful to remove the paper, turn the stack over and put it back in the paper cassette.
Reduce the amount of paper in the paper cassette, and then try again.
Make sure you use paper that meets Brother's recommended paper specifications.
Reinstall the paper properly, and then press the control panel button. The
printer will start printing again.