There are 2 separate options to sell tickets for an event to a limited audience:

The pre-sale feature lets a targeted audience buy tickets before the event opens to the general public. You can create as many passcodes as you need, and each one only works during its own start and end date. This makes it easy to run staged pre-sales, like a donor code one day and a member code the next.

You can also let qualifying patrons in with just their email address, no code needed. Patrons can qualify through a membership, a group or organization, or a list of email addresses you enter. When a patron unlocks the pre-sale with their email, that email is filled in on the checkout form and can’t be changed, so the tickets stay with the person who qualified.

Please see this discussion on how to set up a pre-sale:

Requiring a coupon code at checkout is useful for limiting event access to a targeted audience or for giving early access to Flex Pass holders. You can create unique or shared codes to restrict purchases, and optionally set the event to semi-private for added exclusivity. Only people with a valid code can buy tickets, and for Flex Pass users, the required code is automatically included in their voucher link.

Please see this discussion on how to require a coupon code at checkout: