Not RIFF WAVE

I’m trying to add a track to my SD Card, under /tracks.
I ensured the name I’m referencing in the config file is the same as the sound file. But, for some reason, I get no sound at all.
I also ensured the sound file is a .wav with 41KHz, 16-bit, Mono PCM.
When opening the serial monitor, navigating to the font and triggering the track, this appears:

Not RIFF WAVE.

Does anyone know what this means? Is there some special type of WAVE file I need to use? What is RIFF?

I tried vegas pro, audacity and online converters, to convert the source mp3 to a WAV file for Proffie. No success.