Size the gift for the fees
Before deciding an amount, look at a real listing for the kind of event they would go to and note the difference between the headline price and the total at checkout.
Adding roughly a fifth to whatever you think the tickets cost is a reasonable starting point. A card that covers exactly the face value of two tickets will not buy two tickets.
Availability, not money, is the constraint
For popular events the limiting factor is getting through the queue, not paying. A gift card does nothing for access — presenting it as a way to secure tickets to a specific in-demand show sets up a disappointment.
Frame it as "towards tickets", not "for those tickets".
Expiry and timing
Credit typically carries an expiry, and the events somebody wants may not go on sale within that window. For a recipient with a specific artist or team in mind, check roughly when tickets usually go on sale before buying.
Resale listings
The platform hosts resale as well as primary sales. Whether credit applies to resale listings varies and is worth checking rather than assuming, because resale is often where the tickets actually are.
Delivery and transfer
Where tickets are mobile-only and tied to an account, the person who books needs to be the one who attends or must transfer them. Not a gift card issue as such, but it shapes who should do the booking.
Region
Country-specific. Confirm the country the account is in.
Asking for one
Country, amount, and the kind of event if you know it. See experience gift cards explained.