You can activate a notification during sale to alert the seller about the mandatory membership fee/medical certificate required for the selected multipack. In order to do so, go to Planning -> Multipacks -> Access Types -> Detail -> Access and tick the required box.

In case the user who is purchasing that multipack does not have an active membership fee/valid medical certificate, a pop-up window will alert the seller during the sale procedure.

It is still possible to force the sale ignoring the alert.