The invitation is two things
First the message: a few lines in an inbox, a chat, or a newsletter, short enough to survive being read standing up. Its only job is to earn the click. Second the page it points at, which has the harder job of turning a click into a name on a list.
Most failed invitations are not bad writing; they are a mismatch. A message promising one thing, a page organised around another, and a reader who notices the gap. The fix is to decide on the promise once, then repeat it in the message and honour it on the page: same headline idea, same agenda, same time.