Try using a different browser and turning off ad-blockers and pop-up blockers.
Under certain circumstances, some people might experience problems downloading conversions done in Projects. The common denominator for this seems to be the browser where most people are using a browser called Brave, which is causing issues for them. However, we've also heard certain users experience issues with other browsers. In most cases, the issue seems to be resolved when they switch or test a different browser to download the files. We also recommend turning off any ad-blocker or pop-up blocker.
If you're having issues downloading in Projects, make sure you are following the correct flow as you don't download audio in Projects the same way you're doing Speech Synthesis. After you've converted your chapter(s) Projects. You download it by going to Convert -> Versions -> Download, which is different from how you would download an audio file in speech synthesis, where you do it from the play bar.
If you've made any changes to the project since last converting it, you will need to reconvert the project. It will say how many characters will need to be converted and how many credits it will cost you as this also assembles the full audio for you so it can be downloaded in a single continuous file.