# Fleet Fuel Card Controls API > Detect fuel card misuse from caller-supplied transactions, vehicle tank capacity, fuel type, odometer readings, and locations. Flags impossible volumes, duplicates, shared cards, capacity overflows, and unreachable purchase locations with deterministic evidence. Each POST has a fixed USDC price on Base, paid with the x402 exact scheme. The request is validated first, and payment settles only after a successful (2xx) result. Failed calls are not charged. 1. POST JSON matching the requestBody. Invalid input returns 400 with no payment challenge. 2. A valid unpaid call returns 402 with the exact amount and payTo. 3. Pay and retry with payment-signature. Payment settles only if the operation returns 2xx. A 4xx/5xx is not charged. - Product: https://www.brainiac.software/api/fleet-operations - Docs: https://www.brainiac.software/api/fleet-operations/docs - OpenAPI: https://www.brainiac.software/api/fleet-operations/openapi.json - Contact: support@brainiac.software (https://www.brainiac.software/contact) ## Operations ### POST /api/v1/fleet-operations/fuel-card-abuse-detect $0.04 USDC. Flag fuel card transactions that exceed tank capacity, mismatch fuel type, duplicate within a time window, share one card across vehicles, overflow the tank without mileage burn evidence, or appear too far from the vehicle for the supplied max speed. Volumes are millilitres. Every flag includes deterministic evidence. No telematics or merchant network is queried. Inputs: vehicles, transactions, odometer_readings?, locations?, duplicate_window_minutes? Docs: https://www.brainiac.software/api/fleet-operations/docs#fleet-operations-fuel-card-abuse-detect Example request: ```json { "duplicate_window_minutes": 120, "vehicles": [ { "id": "v1", "registration": "AB12 CDE", "fuel_type": "diesel", "tank_capacity_ml": 60000, "expected_consumption_ml_per_km": 80, "max_speed_meters_per_hour": 120000 }, { "id": "v2", "registration": "XY99 ZZZ", "fuel_type": "diesel", "tank_capacity_ml": 50000 } ], "transactions": [ { "id": "t1", "card_id": "card-1", "vehicle_id": "v1", "purchased_at": "2026-11-05T08:00:00.000Z", "volume_ml": 40000, "amount": 6000, "currency": "GBP", "fuel_type": "diesel", "station_id": "s1", "latitude": 51.5, "longitude": -0.12 }, { "id": "t2", "card_id": "card-1", "vehicle_id": "v1", "purchased_at": "2026-11-05T09:00:00.000Z", "volume_ml": 40000, "amount": 6000, "currency": "GBP", "fuel_type": "diesel", "station_id": "s1", "latitude": 51.5, "longitude": -0.12 }, { "id": "t3", "card_id": "card-1", "vehicle_id": "v2", "purchased_at": "2026-11-05T09:30:00.000Z", "volume_ml": 20000, "amount": 3000, "currency": "GBP", "fuel_type": "diesel", "station_id": "s2" }, { "id": "t4", "card_id": "card-2", "vehicle_id": "v1", "purchased_at": "2026-11-05T18:00:00.000Z", "volume_ml": 70000, "amount": 9000, "currency": "GBP", "fuel_type": "petrol", "latitude": 52, "longitude": 0.5 } ], "odometer_readings": [ { "id": "o1", "vehicle_id": "v1", "reading_km": 1000, "recorded_at": "2026-11-05T07:00:00.000Z" }, { "id": "o2", "vehicle_id": "v1", "reading_km": 1005, "recorded_at": "2026-11-05T17:00:00.000Z" } ], "locations": [ { "id": "l1", "vehicle_id": "v1", "latitude": 51.5, "longitude": -0.12, "recorded_at": "2026-11-05T17:30:00.000Z" } ] } ``` Example response: ```json { "flagged_transactions": [ { "transaction_id": "t4", "vehicle_id": "v1", "card_id": "card-2", "code": "impossible_volume", "suspected_loss_amount": 9000, "currency": "GBP", "evidence": [ "Purchased volume_ml 70000 exceeds tank_capacity_ml 60000 for vehicle v1." ] }, { "transaction_id": "t4", "vehicle_id": "v1", "card_id": "card-2", "code": "fuel_type_mismatch", "suspected_loss_amount": 9000, "currency": "GBP", "evidence": [ "Transaction fuel_type petrol differs from vehicle fuel_type diesel." ] }, { "transaction_id": "t2", "vehicle_id": "v1", "card_id": "card-1", "code": "duplicate_purchase", "suspected_loss_amount": 6000, "currency": "GBP", "evidence": [ "Transaction t2 is within 120 minutes of t1 for the same vehicle.", "Both name station_id s1.", "Same card card-1 was used twice inside the window." ] }, { "transaction_id": "t2", "vehicle_id": "v1", "card_id": "card-1", "code": "capacity_overflow_without_burn", "suspected_loss_amount": 6000, "currency": "GBP", "evidence": [ "Cumulative purchased volume before burn evidence is 40000 ml plus 40000 ml, above tank_capacity_ml 60000.", "Insufficient odometer span was supplied to justify burn between fills." ] }, { "transaction_id": "t4", "vehicle_id": "v1", "card_id": "card-2", "code": "capacity_inconsistent_with_mileage", "suspected_loss_amount": 9000, "currency": "GBP", "evidence": [ "After accounting for 5 km at 80 ml/km, remaining tank room is at most 20400 ml.", "Purchase volume_ml 70000 exceeds that room against tank_capacity_ml 60000." ] }, { "transaction_id": "t3", "vehicle_id": "v2", "card_id": "card-1", "code": "card_shared_across_vehicles", "suspected_loss_amount": 3000, "currency": "GBP", "evidence": [ "Card card-1 fueled vehicle v1 at 2026-11-05T09:00:00.000Z and vehicle v2 at 2026-11-05T09:30:00.000Z inside the duplicate window." ] } ], "summary": { "transactions": 4, "flagged_transactions": 3, "flag_count": 6, "suspected_losses": [ { "currency": "GBP", "amount": 42000 } ] }, "explanations": [ "Volumes and tank capacities are millilitres. Amounts are integer minor currency units. No unit conversion is invented.", "impossible_volume flags any purchase above the vehicle tank_capacity_ml.", "duplicate_purchase and card_shared_across_vehicles use duplicate_window_minutes (default 120).", "capacity_inconsistent_with_mileage requires expected_consumption_ml_per_km and odometer readings; consumption is never assumed.", "suspicious_location compares purchase coordinates with the nearest supplied vehicle location using rounded haversine meters and max_speed_meters_per_hour.", "Every flag includes evidence strings. No external telematics or merchant network is queried." ] } ```