There isn't a setting that would require adding a customer prior to finishing the sale. I can see how that would be useful in ensuring that you wouldn't miss any names; I'll share the feedback product liaisons team.
You can enable the ability to add a Customer before and after checkout, which will at least present another opportunity to add a customer. If you don't have both enabled already, you can so so from in the app: Settings > Customer Management. Hope that helps!
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