The TM-6 PRO will display "Unsupported Format" if you attempt to import an audio file that isn't compatible.
The TM-6 PRO can import .WAV files that are 16 or 24 bit with a sample rate of 44.1kHz.
Make sure files are transferred to the import folder on the SD Card. (Do not place them into any folders that may be on the SD Card). Also note that the SD card must be formatted in the TM-6PRO first before transferring any files.
Audio that was purchased from an online music store such as Amazon or iTunes, or ripped from a CD, are commonly MP3 (compressed) or m4a audio files and will not import into the TM-6PRO. You can use iTunes, Windows Media Player, Audacity or other free programs available on the internet to convert these files to .WAV. Refer to the program's documentation on how to perform this conversion.
If you're sure you have file that conforms with the specifications mentioned above, and it still won't import into the TM-6PRO, then the file may have embedded metadata, or "tags," that are causing the error. This can happen with files that have been created by 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. Here is a link to an Knowledge Base article that shows how:
https://www.roland.com/us/support/knowledge_base/201977529/