There are a few reasons why it may not work & how to make it work!
Your lips and mouth muscles are too stiff to pucker deep into the pump. Try to practice puckering 10 times before using the pump. Pucker your lips as far out as you can. This action works 34 facial muscles. Do lip yoga or lip gymnastic before your attempts.
You must have complete contact—meaning air-tight between the lip-shaper mouthpiece and your mouth. If you cannot use the pump hands-free at first, hold it until you learn to use it hands-free.
Your pump might be too large for you. In this case, use the mouth cover to help you create a tight-seal between your mouth and the pump.
Your pump may be too small for you. Remember to buy the right pump for your lip width.
The pump may have an air-leakage issue. A good way to check if your lip pump is working properly is to swallow some air while you plump. If you gradually lose suction like a deflating balloon, you may have a defective plumper.
If your lips are non-responsive or resistant to plumping, try 1 lip at a time. Add a blocker and a mouth cushion before you plump.
If it is difficult for you to create a good suction after you add a mouth cushion, try to swallow some air while you plump.
Some users apply Vaseline to the lips or even wet the plumper opening with water as a way to get a better grip on the lips. (For practice only)