A disposable vape pen can stop working for a variety of reasons. Here's a quick walkthrough of possible causes and what you can do.
No airflow
One reason your disposable cart isn't working is that air bubbles may be preventing proper airflow. You should flick or tap the cart to pop the air bubble.
Debris
You can't pull from your vape if its mouthpiece is clogged by debris. Start by checking for tiny pieces lodged in the mouthpiece. If you see any, use a pointy object to dislodge it.
No battery charge
You should see the indicator light turn on every time you pull. If you don't see any, check if the battery has enough power and recharge it if it lacks juice. Otherwise, you may have a defective battery.