How do you make epub files compatible with IOS?

Hi. The website where i read these light novels make epub files for every volume they make, but the first volume they made has part of someone else translation in it so they wont make an epub file for it. So i have an epub for volume 2 and 3 in my book store, but not volume 1. I made a volume 1 epub file by changing the volume 3 epub file into a zip file, open it with izip unarchiver and using it as a template. I want the style of epub book i am make to look like it was made by by the people who made volume 2 and 3. I have successfully made the epub file and my mac pro ibook excepts it with no errors, but I can't open it on my iPad or iPhone. When i try to open the file on my iPad or iPhone i get an error message saying that the file can't be opened. Their volume 2 and 3 epub files work on my iPhone and iPad so now im lost, because i don't know how to make the files compatible on my IOS devices. Does anyone know how i can fix this? Is there is a simulator or scanner i could run my epub through to look for errors for me to fix?

light novel website: https://shintranslations.com/the-new-gate-toc/

I have been using this youtube video as guidance through the process of making the epub: https://www.youtube.com/watch?v=EiUMb7bgYeQ&index=12&list=LLmWNqbDQmsQOrLVA2f-zH iw

I have made a google drive folder that has a zip file with both epud files and the code of each file if there is anyone that wants to look at the code directly. (their's is volume 3 mine is volume 1): https://drive.google.com/folderview?id=0B81CusU078sjYW1QbWRCTEpzWlU&usp=sharing