Your audio file is not a true mp3 file. Did you just rename an m4a audio file with an .mp3 extension? Convert the file to a proper mp3 file at sources like https://convertio.co/m4a-mp3/ and reupload and refresh campaign.

Your audio file is far too long for the video. Try to have your audio no longer than the length of your video, plus 10 seconds.  If you upload a 4 minute audio file for a 30 second video, the app will time out. Edit your clip and re-upload.

Your speed changes contain conflicting instructions.  Check your segments within Speed Changes to make sure you're not asking the system to run the same section at two different speeds. There should be no overlap of clips in Speed Changes.

Your video is too long for the effects requested. A simple video with no effects can be longer than another video with several effects.  Try not to exceed 45 seconds for videos with effects.