Fetch transactions and match receipts via the Ramp API

Steps

1. Register an application in the Ramp developer portal and complete OAuth 2.0 authorization at https://app.ramp.com/v1/authorize; request scopes including 'transactions:read' and 'receipts:read'.
2. Exchange the authorization code for tokens at https://api.ramp.com/developer/v1/token; store both the access token and refresh token — access tokens have a limited lifetime.
3. List transactions with GET https://api.ramp.com/developer/v1/transactions; use query parameters 'from_date', 'to_date', and 'state' (e.g., 'CLEARED') to filter; responses are paginated via 'next' cursor in the response body.
4. To retrieve receipts associated with a transaction, GET /developer/v1/transactions/{transaction_id}/receipts; each receipt object includes a 'receipt_url' for the file download.
5. Upload a receipt to match to a transaction by POSTing to /developer/v1/transactions/{transaction_id}/receipts with a multipart/form-data body containing the receipt file.
6. For bulk exports, use the accounting sync endpoints (/developer/v1/accounting/sync) which batch transaction and GL-coding data in formats suited for downstream accounting systems.