Opt-ins are the words your readers see convincing them to sign up for your email list. Usually, in return for a freebie being offered- aka lead magnet. Opt-in exists to present the lead magnet.

The words you use to capture leads need to

-entice

-present your invitation

-Win over your reads

In only a few seconds in exchange for their cherished email before they're gone, never to be seen again.