The Total PA series of ION speakers include a USB port that supports reading audio files from a USB thumb drive. However, other models may include a USB port that is strictly for charging a phone or similar device. The charging USB port does not support playback of audio files.
If your Total PA is not playing the files, please make sure that the USB drive is formatted to FAT32 or exFAT and the files (MP3s) are in the root directory of the drive. They cannot be inside of folders or the Total PA will not recognize them.