If a completed registration has no attendee type, or the wrong one, it's usually one of the causes below. Without an attendee type, the registration also gets no fee, and emails that depend on attendee type can arrive blank.

A completed registration has no attendee type

1. The attendee type was full. If the attendee type has a capacity, logic can't assign it once that capacity is reached. The registration still completes, but with no attendee type and no fee. Check the capacity under Plan > Event Setup > Attendee Types and raise it if needed. Also check that the event's overall capacity and the attendee types' capacities make sense together.
2. The registrant left the form open too long. While someone registers, their attendee type holds a spot for a set number of minutes after their last change. If they come back after that, the spot has been released and the attendee type and fee can come through blank. Set the time under Plan > Configure > Options, in Incomplete registrations count against Capacity/Inventory for __ minutes after their last modification. The default is 10. You can enter any whole number from 0 to 360,000.
3. Nothing on the form sets it. If the form doesn't ask for an attendee type and no logic rule assigns one, registrations come through without it. Add the attendee type choice to the form, or add a logic rule that assigns it.

Guests get the wrong attendee type

To give guests the same type as the person who registered them, use a logic rule with the condition Primary Registrant Attendee Type. To limit which types a guest can pick, use the Display Attendee Type action. For more than one type in a condition, use the Is One Of operator.

Changing someone's attendee type cancelled their sessions

Sessions are published to specific attendee types. If you move someone to an attendee type the session isn't published for, their session is cancelled. Publish the sessions to the new attendee type first, then change the registrants. If it already happened, re-add the sessions. See How do I reinstate a cancelled session?.

Fix the registration

Open the registration, set the attendee type under Profile > Registration Information, and save. To fix several at once, select them in a registration list and use the mass action Set Attendee Type to the right type. Then check the balance and resend the confirmation email if needed. See Why is information missing from my email, or why is the email blank?.

Next step: Still not right? Contact Support with the event code and the registration code.