I traveled with a soft backpack that fit easily under the seat on my outbound flight, but at the return boarding gate an agent claimed the bag bulged slightly past the personal item metal frame and charged me a $99 gate fee. The bag slipped into the bin without breaking zippers. What is the proper procedure for requesting a refund on an unjustified baggage charge?

Keep your boarding pass and printed credit card receipt showing the exact time and gate location where the auxiliary baggage charge was applied. Take a clear photograph of your backpack resting inside the metal sizer before paying any gate penalty, so an inquiry submitted through the Frontier Airlines phone number later includes photographic documentation to dispute unnecessary baggage surcharges. Submitting a formal baggage fee complaint through the carrier's online portal with those attached images gives customer relations verifiable evidence that your luggage met published dimensional limits.

Thanks for the practical suggestions! I'll keep the receipt and photos and submit a complaint if the baggage charge appears incorrect.