How to list existing transactions
GET /api/v1/txns
GET /api/v1/txns/<transaction_id>
GET /api/v1/txns
limit - limit of number of results to return (default: 100)
offset - offset (default: 0)
order_by - field name to order by (for example: "txn_opened_on")
order_type - “desc” or “asc”
...