You can set that some tours/activites are available only for customers who purchased a prepaid package.
1. Go to Settings>Tours and Activities
2. Click on the specific tour, and go to the General tab
3. In the Package only section, select that customers can make a booking only after purchasing a prepaid package.
How can customers book tours that require the purchase of prepaid credits?
When customers click on that tour/activity, they will be asked to sign in the customer area and buy/use their prepaid package