All I can tell you is how I added my audio to a post. After that, the audio player bar only appears for a brief second then simply goes blank. You can listen to the audio in the post but it brings you to another page where it downloads.
While in a post, I select the Media icon and upload a mp3 file. Once uploaded, I then select the file to be inserted in the post. Then I save the post. I hadn’t downloaded any plugin prior. Afterwards, with it not working properly, I added a plugin for audio but nothing improved.