Make a GET request to /transactions/{transactions_id} where {transactions_id} is replaced with the transactions's id to return a list of transaction hashes.
Multiple transaction hashes means that previous ones have failed, and the transaction system rebroadcasted the event.
Since Tx Relay uses a dynamic gas escalation plan, the transaction hash will update every time a new gas price gets published. In order to avoid providing stale transaction hash data, a list of transaction hashes will be returned to you with all the submissions which have occurred so far.