my irobot m6 mop won't go back to its charging station at the end of a job, it just sits in the middle of the floor.

First, ensure the robot started the job from the charging station. The return-to-home feature only works if it did.

1. Manually send it home. Tap the HOME button on the robot. A blue light ring pattern means it's seeking the station.
2. Check the path. Clear any clutter, loose rugs, or cords between the robot and the station. The station needs clear lines of sight.
3. Clean the sensors. Wipe the front IR sensor window, the cliff sensors on the bottom, and the rear docking sensor with a damp cloth.
4. Verify station placement. It must be on a level surface, against a wall, with at least 1.5 ft (.5 m) of space on each side and 4 ft (1.2 m) from stairs.

If that didn't work, the charging station itself may be unplugged or obstructed. Make sure it's plugged in and the drip tray is attached and clean.