Getting multiple download option to work

Hi,
I am using your plugin on this website https://www.musichouseint.com which I am building for the musician. What the client has asked for is the ability to be able to download multiple files (where one can select one, many or all file) and from what I read in the documentation this is possible. However, I cannot get it to work. So I am not sure if I have added the products correctly (simple product), should it be a grouped product, variable product?
Downloads are working for single products.
Your help would be very much appreciated. Admin access can be granted if needed
Regards Ian

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