I have a Master subscription and have been using it for 3 months in a campaign with my friends. They access the book through me. Since yesterday, they can access the book and all the other purchased content from the app nor the website. HELP! 

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EDIT - Already solving it with support

Did campaign sharing get turned off in the campaign by accident? This would be on the top-left of the page when viewing a campaign. Example:

Thanks. I Just checked and it is indeed enabled. But support already reached out. Thanks