I am another expert on this site. Let me know if you still need help with this as I have a suggestion which might work
Ok one moment please..
Ok try downloading the file again, then after you click Save button you will get a Save dialog box similar to the one shown in this screenshot
Attachments are only available to registered users.
Select the file name in the File Name field and simply change the zip extension to xlsx (so in the example above the file name would be Book1.xlsx). Then click Save and you should be good to go
Hope this helps
You said in your initial question that the xlsx file is coming through as a zip file. Hence my reply addresses that issue so you can download it as an xlsx file
I thought I answered your original question, but if you didn't find my answer helpful I will opt out so the question becomes open