We’ve blogged previously about requiring a specific level to allow registration for another level. In that post, the registration check occurs after the user submits the checkout form. This new code gist immediately redirects away from the checkout page if the user’s current membership level is not ID = 1 or is unset.
Again… why would I want to do this?
As I said in the previous post, some membership sites have a specific workflow for membership. For example, if you have a fitness website with phases of training, you’d want to make sure your customers move through your program in the right order.