Diagnosis
The detergent dispenser drawer is clogged with hardened detergent or fabric softener. The water inlet valves are not flushing the compartments.
How to Fix It
Remove the dispenser drawer. Press the release tab inside the main compartment. Pull the drawer straight out. Soak the drawer in hot water. Use a small brush to clean the siphon caps and channels in each compartment. Flush the housing in the machine with hot water.
If That Didn't Work
The water inlet valve for the dispenser flush may be clogged or failed. Check that water flows into the dispenser housing when the washer is filling. No flow indicates a valve issue.
Heads Up
Liquid fabric softener should only go in the middle compartment marked with a flower icon. Putting it in the pre-wash or main wash compartments will clog the system.