Phone verification

YouTube gates features behind tiers. The intermediate tier opens with a code sent to a phone number, and that is where custom thumbnails, videos over 15 minutes and live streaming sit. The advanced tier needs video or identity verification, or a channel history of around two months, and covers things like appealing Content ID claims and posting more videos a day.

None of this is the tick beside a channel name, which is a separate process entirely. A new creator wondering why the custom thumbnail button does nothing has almost always skipped this step, and the code arrives in seconds once you find the setting.