Use the Wex (formerly EFS) fleet card API to authorise and record fuel transactions for a rental fleet

Steps

1. Apply for WEX fleet card API access through the WEX developer partner program and obtain your API credentials and sandbox environment details.
2. Authenticate requests using the OAuth 2.0 client credentials flow to obtain an access token; include it as a Bearer token on all API calls.
3. Call the accounts endpoint to retrieve fleet account details including card list, spending limits, and vehicle assignments for the fleet.
4. To authorise a fuel or service transaction, POST a pre-authorisation request with the card number (tokenised), merchant category, and requested amount; capture the auth code from the response.
5. Complete the transaction by POSTing the settlement request with the auth code, actual transaction amount, and odometer reading (required for fleet cards).
6. Retrieve transaction history via the transactions endpoint with date range filters for fleet fuel cost reporting and per-vehicle expense allocation.