Can the Portenos here shed some light on why there is this rather arcane requirement to purchase the fee online rather than pay on arrival, as was done in the past? Were agents at the airport stamping passports and forgetting to log the fees? If this is the case, it seems like just setting up a few computers at the airport and charging 50 pesos to use them would have the doubly beneficial effect of getting people into the country, where they could spend money, and providing a lot of 50 peso revenue enhancements to the airport, government, or whomever.