MP3 uploads to Digital DJ Pool must be encoded at 320 kbps CBR (constant bitrate). If your MP3 is variable bitrate (VBR) or uses a different bitrate, export it again as 320 kbps CBR.
WAV files are also accepted, so the MP3 bitrate requirement does not apply to WAV.
Choose your audio software in Creating a 320 kbps MP3 file for export instructions. If your software is not listed or the file is still rejected, contact Digital DJ Pool support with the software name and exact error message.