Go to Admin>Shop Settings>Enforced Coupon=YES

Now we can create a New Discount Coupon in Admin>Orders>Vouchers and Coupons

We can make the discount zero

Don’t forget to enable Discount Coupons for the Orders Totals

Now at checkout a customer is asked to provide a Valid Coupon Code

Those with a valid coupon code can now checkout and purchase their tickets as priority

When you want to open up to the public set Enforced Coupon =NO