How do I enable pay-per-read and subscription options at the same time?
You can grant readers a choice of how to access your paid article.
Readers can either purchase an article individually (pay-per-read), or subscribe where they can access all premium articles for a given term.
In order to do so, you must create at least 1 subscription plan and assign a price to the article.
However, you cannot place an article under a subscription without adding a price to it.