Description of Complaint: I purchased a ticket on April 21 to fly from Washington DC to Amsterdam and from Amsterdam to Düsseldorf. I got the conformation and thought that the only thing left for me was to go to the airport to check in. My flight was on May 5th with KLM. I bought the ticket online from KIWI. When I got to the airport, they told me that they had my ticket in their system from washington Dulles to Amsterdam and From Amsterdam to Barcelona. They refused to get me on the plane even after I showed them my email with my E-ticket which was attached. They said that they could not find any ticket on my name from Amsterdam to Dusseldorf. I lost my flight including $120 that I paid for my COVID test. When I called Kiwi, they told me that I had agreed to get an extra ticket in order to pay less for my flight, but I was not obligated to use the extra ticket. I wasn't aware of that. When I got my online ticket the confirmation was for my flight to Dusseldorf. Now KLM blames Kiwi and Kiwi blames KLM