[Marqeta CoreAPI spec]: For DECLINED and ERROR journal entries, check funding.gatewayLog.message (the gateway decline message), funding.gatewayLog.timedOut (whether the gateway request timed out), and funding.gateway.response.data.jitFunding.declineReason for specific reasons like INSUFFICIENT_FUNDS or CARD_EXPIRED. This field is null on successful PENDING/POSTED entries, so its absence tells you nothing when things work. DECLINED entries are persisted with full details, so pull the journal entry first instead of guessing from the dashboard summary.

Context: A Marqeta transaction shows status DECLINED but the reason is unclear. The decline diagnostics live in the journal entry's funding.gatewayLog fields.