Shokz OpenSwim MP3 headphones and Apple AAC audio files compatibility issue

I purchased some Shokz OpenSwim MP3 headphones to be able to listen to music and podcasts while swimming. The technology is allegedly simple - connect to my MacBook Pro, drag and drop my audio files onto the OpenSwim drive on my desktop. However I am unable to even grab my downloaded podcast files. These headphones can take MP3, WMA, FLAC, WAV & AAC. I've checked the file info for the tracks I'm trying to transfer and they're AAC. Any help appreciated.

I reached out to shokz and they are not helping and simply said to reach out to apple - which I did as I was told, but files are not converting to MP3 as they are protected files.

Really frustrating- why doesn't apple create swimming headphones?

All my products are apple

[Re-Titled by Moderator]