Got another offer via the app today. Book a premium cabin trip (min. $750 fare) and get ~20k miles. Too bad I already booked my travel for the period specified!
I understand their intent might be to encourage you to book a trip that you might have otherwise not taken, but this can be just frustrating when you've already booked the travel: oh, I could have gotten these extra miles but won't. (Of course, close-in F/J bookings aren't often cheap anyway.)