TorBox allows infinite downloads, but unused things are removed after 30 days. This is due to storage space being in high demand. If you are not using your downloads, then the system realizes that it must not be important and removes it from the storage. A few outlined reasons for downloads going inactive are listed below:

Any downloads not downloaded within 30 days of being cached are removed to make space for other downloads. Downloading an item, will reset its time to delete, meaning you will have another 30 days. If someone else downloads the same item, that will also reset its time to delete, giving the item another 30 days to remain on the cache.

If you have just downloaded an item, and it suddenly went inactive, then there might have been an error of some kind. Check on the dashboard, and it will tell you what type of error it was.

To prevent inactive downloads, you must actually download or stream them. Downloading the files will reset the timer on them. Using the webDAV or FTP server does not prevent downloads from going inactive due to the ways that integrations use them.