GitHub · Pull requests · REST API · Checked October 25, 2026

GitHub: why the comment or reply was not posted

A comment in a pull request's conversation is posted with POST /repos/OWNER/REPO/issues/NUMBER/comments (every pull request is an issue), and a reply in a review thread on the diff with POST /repos/OWNER/REPO/pulls/NUMBER/comments/COMMENT_ID/replies. GitHub's documentation lists 201, 403, 404, 410 and 422 for the comment, and 201 and 404 for the reply; creating content too quickly with either can hit secondary rate limits (checked October 25, 2026).

Unable to create comment because issue is locked.
Repository was archived so is read-only.
Body is too long (maximum is 65536 characters)

GitHub's words and the reasons

Unable to create comment because issue is locked. (403): the conversation is locked. GitHub's documentation says that while a conversation is locked, only people with write access and the repository's owners and collaborators can add comments; conversations on issues, pull requests and commits can be locked. A public report from 2026 got this 403 with a workflow's GITHUB_TOKEN and with a GitHub App token that had issues: write; posting from an account with the Write role worked.
Repository was archived so is read-only. (403): the documentation says that an archived repository's issues, pull requests and comments are read-only, and that its conversations are locked automatically. A public report from 2026 met it when commenting on pull requests in archived repositories.
Body is too long (maximum is 65536 characters): a validation failure. Public reports met it from tools that post long generated reports as comments.
An interaction limit: on a public repository, the documentation says, the owner can limit commenting for a while (24 hours to 6 months) to accounts that are not new, to prior contributors, or to collaborators with write access.
404 on a reply: the documentation says COMMENT_ID must be the first comment of the review thread, not a reply; replies to replies are not supported. A comment that no longer exists, or a repository the token cannot see, also answers 404.
The token: in GitHub's list of permissions, a conversation comment is Issues or Pull requests write for a fine-grained token, and a reply is Pull requests write (see which permission to add).

What to do

Locked: ask someone with write access to unlock the conversation, or comment from an account with write access.
Archived: only unarchiving the repository makes it writable again; its owner can do that.
Too long: shorten the text, split it over several comments, or link to the full text.
Interaction limit: wait for the period the owner chose to end, or ask a collaborator to comment.
404 on a reply: reload the pull request so the threads are as they are now, and reply to the thread's first comment.
Many comments in a row: slow down; see "API rate limit exceeded". For a comment on a line of the diff, see GitHub line comment 422.

In IntelliJ IDEA: a reply only when GitHub allows it, and the text stays when it is refused

How the GitHub support built into IntelliJ IDEA replies in a review thread of the pull request's timeline, in its source (checked October 31, 2026; IntelliJ IDEA: GHPRTimelineThreadViewModel.kt, GHPRReviewServiceImpl.kt, GHGQLRequests.kt):

When you can reply: only while GitHub returns viewerCanReply as true for your account on that thread.
It sends a GraphQL request (addReviewComment in its source) that replies to the first comment of the thread, not the REST endpoint above.
When GitHub refuses, the source writes the error to the IDE's log, and the text you typed is not cleared: it is emptied only after the reply goes through.

GitHub pull requests in IntelliJ IDEA

Pull Request Inbox for GitHub, a plugin by Lesstep for JetBrains IDEs 2024.1 or later, posts a conversation comment to the pull request's issue comments, and a reply on the diff to the first comment of that thread. When a reply gets 404, it says the thread's first comment may have been deleted and, if it is still there, that the token cannot write here; it does not put a 404 down to the token alone. Above the comment box it says when the repository is archived (read-only, so GitHub takes no comments) or the conversation is locked (only people with write access can comment). Other refusals are shown with GitHub's words: a refused comment stays in the box, and a refused reply is copied to the clipboard, so the text is not lost. The review inbox, diffs and conversations are free; approving, commenting and merging are Pro (US$1.50 a month, with a 30-day trial).

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