I finally got it working, please read! This is some sort of bug in Hyperpad.
I tried the exact same method on my old IPad and it worked perfectly, no black background! So it works on my older IPad, but not on my newer one. They are both running Hyperpad version 2.0 (20) so I think this is some sort of IOS thing.
My new Ipad is on IOS 18.1.1 and every time I imported, the sprites had black backgrounds
My old Ipad is on version 15.7 and the importing of the sprites worked with no issues despite me doing the exact same method and using the same files.
This may not be the actual issue, but it's the only thing I noticed that was different between my attempts. I guess something in the new IOS update causes sprite importing to not work properly. Please fix! And thanks for this awesome app.