I have made this dish a number of times and am still working on perfecting the crunchiness. I think the key is drying the chickpeas as much as possible like the recipe suggests, but this is a great one to follow: https://www.thekitchn.com/how-to-make-crispy-roasted-chickpeas-in-the-oven-cooking-lessons-from-the-kitchn-219753.