That is rather weird.
first off all i would double check if you ahve enough space free on your phone.
If that is the case, i would download it either via pc and then transfere it over to your phone or download it on oppaiman which is the other offical store page.
I managed to download the game but not here but from another site, but that doesn't matter anymore..I just finished the chapter 9 and I was hoping for chapter 10, Trying this game did not disappoint me. And seeing Moon chi from 'My bully is my lover' really hyped me up since I'm supporting Ni chan, well he's brother Filipino.. Filipino's support each other...I appreciate your work Berkili, I'm waiting for chapter 10, well not only me.. please don't left us hanging.