Not sure if it fits in here about Flipaclip, but did you try downloading on a computer? 

not. I only download using a smartphone

1) Do you have a computer you could try downloading the sounds on? In school, at home, etc. This could be a solution for you.

2) Sometimes (from my experience) files don't work the same when trying to download them on a phone. They could be zipped or the phone storage has no space for them or doesn't know what to do with the files etc.