Wait, adjust, or see a vet

Wait if it is an adult, it skipped one or two meals, it looks plump, and the temperatures are right. Offer food again at the next feeding day.
Adjust if the basking spot is under 90°F or the cool side is outside 72–77°F, or the enclosure is new. Fix the heat first; digestion depends on it.
See a reptile vet if it is losing weight, the tail is getting thinner, it is weak or lethargic, or a juvenile keeps refusing food.

Check these, in this order

  1. Temperatures. The basking spot should read 90–95°F and the cool side 72–77°F. Measure with a probe thermometer or a temperature gun, not a stick-on dial.
  2. Age and schedule. Juveniles eat daily; young adults every 2–3 days; adults every 4–7 days. An adult refusing food on day 2 is not refusing a meal it needs.
  3. Shedding. Dull, pale skin means a shed is coming. Juveniles shed every 1–2 weeks, adults every month or two.
  4. The food. Insects should be smaller than the space between its eyes. Waxworms and hornworms are treats; a gecko fed treats may hold out for them.
  5. A new home. A gecko that just moved may need time to settle. Keep handling to a minimum and keep offering food on schedule.