Mastercard's European rollout of First-Party Trust restructures chargeback liability calculus for issuers and acquirers alike, deploying behavioural and transactional signals at the network layer to distinguish deliberate misuse from genuine disputes before a chargeback is filed. For issuers carrying mounting dispute-processing costs and acquirers absorbing merchant friction, this shifts the fraud defence perimeter upstream — reducing operational load but demanding tighter data-sharing integration with Mastercard's decisioning infrastructure.