Roaming APIs are software interfaces that enable different EV charging platforms to exchange the data needed for roaming—so drivers can authenticate, start sessions, see pricing, and be billed across multiple networks. Roaming APIs connect charge point operators (CPOs) with e-mobility service providers (eMSPs) and/or roaming hubs by sharing standardized information about chargers, tariffs, tokens, sessions, and charge detail records (CDRs).
In most European roaming ecosystems, roaming APIs are implemented using OCPI (Open Charge Point Interface).
Why Roaming APIs Matter
Roaming APIs are the technical backbone of interoperability:
– Allow drivers to charge across networks with one contract (app or RFID charging card)
– Increase charger utilization and improve customer reach for CPOs
– Enable accurate billing and settlement by exchanging trustworthy session/CDR data
– Reduce support friction by making session status and receipts available across systems
– Help detect and prevent revenue leakage caused by missing, late, or rejected CDRs
Without reliable roaming APIs, roaming becomes inconsistent, leading to failed authorizations, pricing confusion, and settlement disputes.
What Roaming APIs Typically Exchange
Roaming APIs commonly support these data flows:
– Locations
– Station and EVSE details, connector types, power ratings, availability, geo coordinates
– Tariffs
– Price components (per kWh, per minute, session fees, idle fees), currency, VAT rules, validity windows
– Tokens
– Authentication identifiers for apps and RFID (token status, whitelisting, contract references)
– Sessions
– Start/stop timestamps, kWh delivered, EVSE ID, session status updates
– CDRs (Charge Detail Records)
– Finalized billing records used for invoicing and settlement between parties
– Commands (optional)
– Remote start/stop requests triggered by the eMSP for a driver
How Roaming APIs Work in Practice
A typical roaming flow via APIs looks like this:
– eMSP publishes user tokens (including RFID tokens) to the CPO or hub
– Driver arrives at a CPO charger and authenticates
– CPO platform checks token validity via the roaming API and authorizes charging
– Session events are shared so the eMSP can show progress in the user app
– When the session ends, the CPO generates a CDR and sends it via the roaming API
– Settlement and invoicing happen based on the CDR and the commercial roaming agreement
Key Technical Challenges with Roaming APIs
– Token synchronization: late updates can cause rejected RFID authorizations
– EVSE ID consistency: mapping errors break sessions, reporting, and settlement
– Tariff representation: complex pricing models must be represented consistently across systems
– Data quality: missing fields, timestamp errors, or kWh rounding can cause CDR rejection
– Offline behavior: chargers may run sessions while connectivity is lost, then sync late
– Security: API credential rotation, IP allowlists, and abuse protection are essential
Operational Controls and Best Practices
– Monitor authorization success rate and session failure reasons by partner
– Reconcile sessions vs CDRs to detect missing records and settlement gaps
– Validate tariff publication and versioning to prevent pricing mismatches
– Implement retry logic, idempotency, and clear error handling for CDR delivery
– Use strong authentication and follow security profiles for API integrations
– Maintain clear escalation paths and dispute workflows in roaming agreements
Related Glossary Terms
Roaming
Roaming agreements
OCPI
Charge detail records (CDRs)
RFID authentication
RFID charging cards
Interoperability billing
Revenue leakage detection
Revenue reporting
Public charging networks