We will need more information in order to help you. Is this a zip file that you uploaded personally and know is a valid archive? If you download it via the ShareFile web app or another tool (ShareFile Sync, ShareFile Desktop, etc.), are you able to extract it?
Please also describe which API endpoint you're calling and the parameter values you're passing. A network trace (e.g., one captured by a tool like Fiddler) would be ideal to help us troubleshoot.
If possible, please also provide the account ID (or the account's ShareFile subdomain) where you're having issues, as well as the item ID of the zip file in question.
If you are uncomfortable sharing any of these details on this forum, feel free to provide them to me in a text file via this ShareFile share: