DIAGNOSIS The detergent dispenser latch is either mechanically jammed or the wax motor that releases it has failed.
FIX Manually open and close the dispenser door several times. Check for a small piece of dried detergent pod film or a bit of plastic wrapper jammed in the hinge or latch. Clean it thoroughly with a damp cloth and a toothpick. Run a test cycle with the door open (watch it) to see if the latch mechanism attempts to move.
IF THAT DIDN'T WORK The wax motor actuator is likely dead. This is a very common failure. You can confirm by listening for a faint click about 20-30 minutes into a cycle—if you hear nothing, the motor isn't getting power or is burnt out. This part needs replacement.
HEADS UP Using liquid gel instead of pods can sometimes gum up the mechanism over time. If you switch to gel, run a cleaning cycle monthly to prevent buildup.