A sheet has stopped in the paper path, or the printer reports a jam even when you can't see one. Clearing it the right way avoids torn paper and roller damage.
Work through these in order; most people are fixed by the first two or three.
Turn the printer off. Pull jammed paper slowly in the direction of the paper path (usually the way it feeds), using both hands to avoid tearing.
Open the rear door, duplexer and toner/cartridge area and look for small torn pieces. Even a tiny scrap triggers a jam message.
Fan the stack, don't overfill the tray, and set the guides snug against the edges. Use the correct paper size/weight.
Wipe the feed rollers with a lint-free cloth lightly dampened with water. Dusty rollers slip and cause repeat jams.
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