I can help here! I work in iOS almost exclusively and there are apps that handle zip files. i use Zip Tool in conjunction with the Files app native to iOS 11 and up. There are many out there.
Click the link above to open the Dropbox website or open the Dropbox app. Either way works. In the app the dot dot dot … is upper right. Choose Export. The share sheet pops up. Choose Copy to Zip Tool or whatever Zip app you have. Zip Tool prompts on open if you want to unzip. Now those files are available to open in Audulus.
If you want to save the zip file to your iCloud storage that’s another way. The Files app has a zip file browser build in, no unzipping necessary. This can be tedious. The file becomes openable in Audulus one by one and takes some time to browse. This tedium is why I use Zip Tool. I browse the entire list faster.
On the website, choose continue to website on the landing page. Again upper right … and choose Direct download. Again, choose the share sheet and either Save to Files which saves to iCloud or copy to Zip Tool and proceed as mentioned before. Hope this helps!
iOS is quite file friendly these days with use of iCloud and the Files app.