Hi, the OFP ID returned by the API is only available when a flight is generated through the API. It can be thought of as an alias, the ID used internally by SimBrief is actually the request_id.
The easiest way to save a reference to the user’s OFP data might be to save the XML data file URL in your database (xml_file in the latest flightplan response). Or even better, save the full OFP data (or a portion thereof) in your database so that it remains available to you, even if that OFP is deleted from SimBrief (OFP data can be removed from the server a few days after the OFP is generated).
Normally each SimBrief OFP is kept on the server for at least 4 days. However, this can be longer depending on how often the user logs in to their account and whether they have generated any subsequent OFPs.