Ack! You ended up with a “backless” dress. I’ve been reading that invisible zippers can seperate and break much more easily that regular zippers, hence my hesitation.
Just thinking that over, probably the best place to put an invisible zipper is in the side seam, where there would be less direct pressure on it than in the center back, where the spine bends outward against it, like when getting out of a car or sitting in an upholstered chair.