First, choose the tickets you want to invalidate and use Batch action to go to Invalidate:

If needed, you can invalidate one or more tickets of the attendee. You have three options when invalidating:

• Automatic refund:

 the amount is automatically refunded to the attendee. This option is only available when an attendee purchases the tickets online using iDeal or via a credit card.

• Manual refund:

 you can use this option to refund with cash or another manual way.

• Invalidate without refund:

 you can use this option to refuse access and decide not to refund.

If you invalidate tickets through the dashboard, you can choose whether to refund the total amount or only a part of it, or if the tickets should be available again or blocked. If you don't select anything, the tickets will automatically be blocked in the category ' Uncategorised'.