Momondo Price Difference Credit Cards
On Google Flights I have been pricing a trip for June-July with the following itinerary: MXP - SIN - AKL - SIN - MXP in Biz. If I use the Italy Momondo site I get just about the prices I get on Google Flights (2507 EUR), no matter what payment method I use. But if I try to book on the Spain (where I live) Momondo site, I get the same price if I pay by debit card, but 4246 EUR if I pay with AmEx. Is this just a glitch in the Momondo system or is there another explanation? Thanks!