Courses and bundles can both be great ways to sell your sessions in bulk but which will suit you best depends on your situation.
Where you are wanting to sell a fixed block of specific classes in a single transaction, for example 6 weeks of session on a Wednesday at 7pm starting on a certain date, that would be sold as a course. This allows your customers to go through a single transaction booking the course that then books them in to every session contained within.
For scenarios where you want to allow customers freedom to pay up front for an amount of sessions but pick and choose the sessions they book within a time frame then you would do this by creating and selling a bundle. Customers will purchase the bundle, essentially pre-purchasing the configured number of credits that they then redeem as payment against the session they want (in line with any restrictions you may have in place, such as valid payment options and package tags).
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