This is the one thing that might make it acceptable to me, but it also begs the question: Who is opting in to getting spammed? (Intentionally, I mean; I'm going to assume you're not using dark patterns to pull one over people while still claiming to be "opt-in")
Generally they're opting in to save money and get good deals at their favorite eating establishments. For some, getting this via text is a preferred method and less friction than downloading an app or alternative medium.
> I'm going to assume you're not using dark patterns to pull one over people while still claiming to be "opt-in"
these wouldn't hold up very well in a lawsuit even if you wanted to do this