Audio file doesn't upload

I have successfully uploaded four .m4a files into my presentation, but when I tried to upload another one of the same format, the wheel spins and nothing happens. I have tried to close Prezi and restart it, same thing. What could be the problem and how can I solve it? I have Edu Plus.
Thanks for your help.

Hi @Dominique_Benson, Please make sure that the codec of the audio file is the same as the first four.

Here is an article about adding audio, hope this helps!