Your printer can show the paper jam error despite there being nothing stuck to its parts. You may have overfilled its paper tray or may not have cleaned the device for long. It might be helpful to completely clear the tray and fill it again with the right type of sheets. In addition to this, you may also properly clean your machine.
Since the cause of this error can be anything but not really a paper jam, you might also go through this link to know more: https://www.errorsdoc.com/hp/how-to-fix-hp-printer-paper-jam-error-but-no-paper-jam/