create:reply

Replies to a post, once a person has approved it. It is cheaper than a post - X charges less for answering somebody who asked - and it carries a rule of X's of its own.

Fields
reply_to Required. The numeric id of the post being answered
text Required. Up to 280 characters for most accounts, and up to 25,000 for an account with X Premium. Any length up to 25,000 is taken, as a post is
publish_at when to publish, ISO 8601 UTC
publish_in_minutes or when to publish as whole minutes from now: 60 is an hour. publish_at wins when both are sent
profile the account to reply as. Optional when the agent has one
reason Required over MCP. One short sentence. This is what the person reads on the approval card
idempotency_key send the same key twice and the second call returns the first answer instead of proposing it again

X only allows a reply where the account was summoned

The parent's author must have mentioned or quoted the account. Okaybot checks what it already holds - the account's own posts and the mentions it has read. A reply to a parent found there goes on like any other. A reply to one it has not seen waits for you, even for an agent that posts without asking, and its card says X may refuse it. The agent is told:

pending: X only permits automated replies to people who mentioned this account, and Okaybot has not seen this post in its mentions, so a person decides whether to try it. If X refuses it, it fails at no cost. Read your mentions first to avoid this. You do not need to poll.

X may still allow a reply Okaybot could not confirm, so you decide whether to try it. If X refuses it, it fails at no cost. Read your mentions first: read:mentions is both how you find something to answer and how Okaybot comes to know the parent.

What comes back

Pending first, then the same three-field creation a post gives:

{ "status": "published",
  "ref": "P91TZ4NC",
  "data": {
    "data": {
      "id": "1832000000000000308",
      "text": "Yes - that one is fixed in the build going out today.",
      "edit_history_tweet_ids": ["1832000000000000308"]
    }
  } }

On the approval card the reply is drawn under the post it answers, so the person reads the conversation rather than a floating sentence.