If the printers isn't detecting paper in one of the trays please follow the below steps
1. Remove all paper from the tray.
2. Remove tray from printer and check for any for any paper jammed behind the tray.
3. Reinsert tray into printer but don't push the tray into the printer fully.
4. Restart the printer (with the tray still pulled out).
5. After the printer has restarted push the tray back into the printer.
6. if the printer still doesn't detect the paper in the tray please contact support.