The RT-MicS can import .wav files that are 16 or 24 bit, with a sample rate of 44.1kHz.
Audio that was purchased from an online music store such as Amazon or iTunes, or ripped from a CD, are usually MP3 (compressed) or m4a audio files and cannot be played by the RT-MicS. You can use iTunes, Windows Media Player, Audacity or other free programs available on the internet to convert these files to .WAV. Refer to your program's documentation on how to perform this conversion.
If you're sure you have a .wav file that matches the criteria above and it still won't play in the RT-MicS, then the file may have embedded metadata, or "tags," that are causing the error. This can happen with files that have been created in DAWs ("Digital Audio Workstations"), other audio programs, or sample libraries. You can strip this extra information from the file by converting it to Apple Lossless or FLAC format. After converting to Apple Lossless or FLAC, convert that file back to .wav 16 or 24 bit / 44.1kHz.
iTunes can be used for these conversions: Convert a song to a different file format with the Apple Music app or iTunes for Windows (Apple website)