Sites like Restore.Media or Online Converter specialize in fixing M4A files that were cut off (e.g., phone died during recording).
If the file won't play, it is likely missing its "header" (the data that tells a player how long the audio is). You can try these methods: RecordTMP (32) m4a
This can sometimes bypass a corrupted header and pull the actual audio out. Sites like Restore
Apps like GarageBand or Audacity may create .tmp or RecordTMP files while you are recording to ensure data isn't lost if the program closes unexpectedly. How to Access or Fix the File Apps like GarageBand or Audacity may create
Because these are often "temp" files, they may not play in standard apps like iTunes or Spotify if the recording app crashed before saving the final metadata. Common Sources of "RecordTMP" Files
VLC Media Player can often play "broken" or unfinalized files that other players can't. Import as "Raw Data" in Audacity: Download Audacity . Go to File > Import > Raw Data .
If the file doesn't have a proper dot before "m4a," try renaming it to RecordTMP (32).m4a to see if your computer recognizes it.