A recording failed. What now?

Click "Try again" (the circular arrow) on the row. For M4A, MP4, MOV, AAC, AIFF, CAF and WebM files the button is not shown, because those are decoded when you add them: remove the row and add the file again. If the error says "could not decode", the file is damaged or in an unsupported codec; convert it to MP3 or WAV and add it again. If the error mentions a link, check that the link is public and still online.