KLM ATL-AMS on 12.26.2023 delayed 3+hours. Requested and approved compensation. KLM offered €500 voucher (do not think I can cash it in). Yet KLM website states compensation for 3+ hour delayed flight to Europe, non refundable ticket is €800. Which amount is correct? Can it be cashed in. If not can I use voucher directly on Delta or does ticket have to be purchased in KLM site?