Help them find the right show.
Include the city and full date
Festival editions can share a name. Your post’s city and event date distinguish the exact show; do not rely on the festival name alone.
Describe the stage or meeting area
Use the place where you actually talked: a stage, queue, concession area, or the walk to the exit. Approximate times are useful when you do not remember the exact song.
Keep one detail for the reply
Ask about your conversation or a small shared moment. Leave the answer out of the public post, and treat a correct reply as a clue rather than proof.