kaeista

so im trying to figure out how to use the transdimesional trapdoors, when i opened a pocket dimensional and tried to us the trapdoor to get back to there overworld.. it just closes and nothing happens.. and no matter how i try it.. it wont stay open and i cant go through it.. i even went down a few levels and still nothing.. can someone people tell me why this is happening and how i can fix this?