Dip a qtip in some alcohol (I keep a small prescription bottle with alcohol just for cleaning vape gear). Get as much of the alcohol off the qtip as you can, so that it is damp, not saturated. Clean the top of your battery where it connects to your topper. Clean your charger where it connects to the battery. Make sure contacts are dry before you connect the battery to the charger.
Try a different coil. Dud coils are a fact of life if you are using premade coils. We have not had a great deal of problems, but we have received a dud coil once in a while.
If that does not help, you may need to use a pin or a small screwdriver to pry up the center pin on your battery. MAKE SURE THE BATTERY IS TURNED OFF if you are using something metal. Gently pry up the center pin a little bit.