not at all, you remove the plug and fill it, replace plug and vape, what device are you using, what voltage, also what kind of juice.
what you can do just in case during production the inner plug was pressed in, you can take a tool or tweezers or small eyeglass screwdriver, and gently lift the inner plug so that the slots thats are cut out on the inner plug on both sides is lifted a little so you can see more of the slit in the cup, the replace your mouth peace and vape. this will alleviate any closure that the inner plug may have caused allowing juice to get in and do its job, other then that these are simple as you get.
let us know if that works out for you and we will help you out if it didnt