You can set up a 2 for 1 offer by creating a 50% Discount and setting a Basket Validation Rule on your Price Table that limits the applied Discount to 2 Tickets in a basket.
This will mean that when the Customer applies the Coupon Code, it will make the basket amount 50% off the price of 2 Full Price Tickets.
The same offer can also be built as a 100% Discount on one of the two Tickets, so the second Ticket is free rather than both being half price. The Basket Validation Rule works the same way for either - choose whichever matches how you want the offer to read to your Customers.
NOTE - you can also use a Basket Discount to take an amount off the basket, but its rules work on the basket's total value, not the number of Tickets.
It only gives a true 2 for 1 when every Ticket in the offer is the same price, e.g. for £30 Tickets, a rule taking £30 off a basket of £60.
Each extra pair needs its own rule (rules are read top to bottom and the first match applies, so put the highest threshold first).
If your Tickets are different prices, use the Discount and Basket Validation Rule below instead.
Basket Validation Rule
Go to your Event's Price Table
Create a New Basket Validation
Set a Rule that the basket:
Must have at least 2 Tickets from your chosen Discount
Can't have more than 2 Tickets from your chosen Discount
Only if the basket has at least 1 Ticket from your chosen Discount
This means that when the Customer adds 2 Full Price Tickets to the basket and applies the Coupon Code, it will turn the 2x Full Price Tickets into 2x 50% discounted Tickets.
Learn more - Overview & FAQs: Basket Validation
Applying the Discount on the Box Office page
On the Ticket page, click Add Discount either:
Before you select any Tickets, and select the discounted prices to add to your basket
Or after you select the Full Price Tickets, and the Discount will take the price off the basket value
Depending on which of the two Discount options you set up, it will take either 50% off both Tickets or 100% off one Ticket