Frequency and spend challenges are the two recommended places to start, because the decision between them comes down to one question: what KPI are you actually chasing?
If your goal is average ticket, build a spend challenge. Spend can be read either as a single check total or as cumulative spend within a window — choose whichever matches the behavior you want. Either way, set the spend bar above your current average, not at it. If your check average is already $43, asking someone to "spend $50" isn't meaningfully different from what they already do; the threshold only works if it stretches behavior. A $50 target might make sense for a sub-$10 coffee concept and be pointless for a $43-average full-service concept — calibrate to your own numbers.
If your goal is building a regular visiting habit — especially during a specific day part — use a frequency (visit) challenge instead, e.g. "visit 3 times within 30 days." This is the better tool when the problem isn't ticket size, it's that people aren't coming back often enough.
Know your own PMIX, COGS, and sales data before picking either one. Look for where your ups and downs actually are — a consistent Tuesday dip, for example — and build the challenge to target that specific gap rather than guessing.