Will resolve according to this Polymarket: 

https://polymarket.com/event/us-x-iran-diplomatic-meeting-by-329

This market will resolve to "Yes" if there is a diplomatic meeting between representatives of the United States and Iran by the listed date, 11:59 PM ET. Otherwise, this market will resolve to “No”.

A diplomatic meeting refers to a deliberate meeting between representatives of the listed countries who are acting in an official capacity and are authorized to engage in negotiation or diplomacy regarding US-Iranian relations on behalf of their governments. Meetings conducted indirectly, for example, through designated mediators, facilitators, or interlocutors acting with the knowledge and authorization of the relevant governments, will qualify. 

Brief greetings, chance encounters, or talks otherwise not deliberately aimed at diplomacy or negotiation will not count.

The meeting must be in-person (including indirect in-person meetings) and must be publicly acknowledged by either government or reported by a consensus of credible media. Remote meetings, phone calls, or other meetings where the relevant parties are not present will not count.

The resolution sources for this market will be official information from the governments of the United States and Iran, and a consensus of credible reporting.