Here are your parts
Replacement parts for WHIRLPOOL GU1500XTLS3 | AppliancePartsPros.com

Here is the tech sheet
https://www.servicematters.com/d...0Sheet%20-%208537797.pdf

And a service manual
https://secured.whirlpoo...0ef763c85256cbc00520548/$FILE/8178022.pdf

Problem can be due to 3 causes:
1. Mechanical
2. Dispenser assembly solenoid/motor is shot
3. Dispenser is not receiving power from the control when it should.

Remove the inner door panel and check the detergent assembly for a visual mechanical fault. Also check the wires going to the solenoid/motor on the dispenser.

Check the release motor resistance, see the tech sheet, if open (infinite resistance), the dispenser will have to be replaced.

Run the diagnostics.

If you do not own a meter, I would suggest you purchase a one. You can get a decent digital multimeter for under $20.00. You do not need fancy though it is nice if the leads are a couple feet long.
If it saves ordering one unnecessary part it has paid for itself and you end up owning a useful tool.
Most places will not let you return electrical parts so if you order it, you own it.
A couple things to watch when measuring ohms and continuity
1. Always remove power from the machine otherwise you could blow your meter.
2. Always disconnect at least one side of any device you are checking. This eliminates the possibility of measuring an alternate/parallel circuit path.
3. When checking for closed contacts and continuity use the lowest scale (Usually 200 ohms). Then try higher scales. This scale is 0 to 200 ohms so if the device you are measuring is 300 ohms this scale would show an open circuit which it is not, you are just measuring outside the scale's dynamic range.

There is a good STICKY at the start of this forum about it's use.