Discord error 40060: Interaction has already been acknowledged

You sent a second initial response to an interaction that already had one. Every interaction gets exactly one initial response through POST /interactions/{id}/{token}/callback, whether that is a message, a deferral, a modal, or an update. After that, anything further must go through the follow-up webhook routes (PATCH .../messages/@original or POST /webhooks/{application.id}/{token}). Calling the callback endpoint twice produces 40060.

In library terms this is reply() after deferReply(), reply() twice in one handler, or showModal() after a reply. It is the mirror image of 10062: 10062 is "you were too late to acknowledge", 40060 is "you acknowledged twice". Developers who fix 10062 by adding a defer at the top and forget to change the later reply() to editReply() move straight from one error to the other.

A subtler source is duplicate event delivery: two processes (a dev instance and a prod instance with the same token, or two shards overlapping) both receive the interaction and both try to respond. The first wins; the second gets 40060.

The broken and fixed versions differ by one method name:

// discord.js - wrong: two initial responses
await interaction.deferReply();
await interaction.reply('done');        // -> DiscordAPIError[40060]

// discord.js - right: defer once, then edit
await interaction.deferReply();
await interaction.editReply('done');

# discord.py - right
await interaction.response.defer()
await interaction.edit_original_response(content='done')

In discord.py the equivalent mistake is calling interaction.response.send_message() after interaction.response.defer(), which raises InteractionResponded locally or surfaces 40060 from the API. Both libraries expose state you can branch on, interaction.deferred and interaction.replied in discord.js, interaction.response.is_done() in discord.py, so shared error-reporting code can pick the correct send method instead of guessing.

{
  "message": "Interaction has already been acknowledged.",
  "code": 40060
}

Structure handlers as: acknowledge once at the top, then only ever edit or follow up. Many libraries expose interaction.deferred and interaction.replied flags; a small helper that picks reply versus editReply based on those flags removes the whole class of bug.

The one-initial-response rule and the follow-up window it hands you are on the Discord limits page; if you arrived here after fixing 10062, the defer-then-edit pattern there is the other half of this fix.

Duplicate-process 40060s deserve an alert of their own, because they mean two deployments share one token and every other interaction is being answered twice.