Anyone we text can reply STOP, and we stop. Immediately, and for every host on SimpleInvite — not only the one whose event they were on.
A plain-English version counts too. Someone who writes stop texting me has opted out as surely as someone who typed the word on its own.
On your event page that person's row says they opted out of texts, and the action beside it becomes Share — you can still carry their invite to them yourself in your own thread, which is a conversation they did not opt out of.
They can turn it back on by replying START.
Opting out of texts is not the same as declining. Their answer, if they gave one, stays exactly as it was.
Email works the same way: a decline link and a don't email me about this event link sit in the footer of every invitation we send.