How can I download my issues with Reader's Digest when each time a pop appears and reads " the item you tried to buy is no longer available"?

I can no longer download my purchased Reader's Digest magazine since August as it requires updating the RD app. So when i try to download the RD app a pop up appears and reads " the item you tried to buy is no longer available". What does this mean and what do I do? I have 2 pending reader's digest issues that needs to be downloaded.

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