https://developers.steem.io/apidefinitions/#account_history_api.get_transaction

Example rpc call:
curl -sd '{"jsonrpc":"2.0", "method":"account_history_api.get_transaction", "params":{"id":"55eb04e397569e27fff8fbf04841ca7c5b9e522c"}, "id":"0"}' anyx.io

Or via RESTful translation:
https://anyx.io/v1/account_history_api/get_transaction?id=55eb04e397569e27fff8fbf04841ca7c5b9e522c