This is most likely one of two things. The first possibility is that you aren't allowing enough time for the flash to charge. It takes at least 5 seconds for this process to take place but even after 5 seconds you must wait for the red light in the viewfinder to turn off before the flash will work again. The camera won't produce an image if the flash is not completely charged. If the red light on the viewfinder is off and it is still not producing a flash then it is likely that the battery that is inside the film pack is dead. In this case you will need to replace the film pack. Polaroid Onestep Close Up Troubleshooting

It is always possible that the temperature is not ideal for the picture to develop. If you are using the film originally designed for the camera then the film is really old and not likely to work. If you are using the Impossible film then the film is very experimental and very sensitive to its surroundings. You don't want it to be too hot or too cold. In the directions of the film is says that at an ideal temperature of 70 degrees Fahrenheit it will take the pictures about 10 minutes to develop. Here are a couple other resources for troubleshooting similar cameras that might help: Polaroid Onestep Close Up Troubleshooting Instax Mini film not developing

This camera has a feature to control the lighting. There is a small plastic piece that is positioned between a white and black arrow. The closer to the black arrow the darker the image. The closer to the white arrow the brighter the image. You should adjust the position of this slider closer to the white arrow and see if your problem is solved. Polaroid Onestep Close Up Troubleshooting