After v4 upgrade: `webhook-type: webhook-trigger` step delivers duplicate messages, then hangs until the job timeout

Description

Hi, we use this action in camunda/camunda (public repo) and noticed a strange behavior: After bumping the action from v3.0.5 → v4.0.0 (no other changes), a step using webhook-type: webhook-trigger began delivering the same message multiple times and then hanging with no further log output until the GitHub Actions job hit its timeout-minutes and was cancelled. Reverting to v3.0.5 resolves it.

What type of issue is this? (place an x in one of the [ ])

• bug
• enhancement (feature request)
• question
• documentation related
• example code related
• testing related
• discussion

Requirements (place an x in each of the [ ])

• I've read and understood the Contributing guidelines and have done my best effort to follow them.
• I've read and agree to the Code of Conduct.
• I've searched for any related issues and avoided creating a duplicate issue.

---

Bug Report

Filling out the following details about bugs will help us solve your issue sooner.

Reproducible in:

package version: v4.0.0

node version: 22

OS version(s): ubuntu:24.04

Steps to reproduce:

Unchanged across the up/downgrade except the action ref:

- name: Send notification
  uses: slackapi/slack-github-action@dcb1066f776dd043e64d0e8ba94ca15cc7e1875d # v4.0.0
  with:
    webhook: ${{ <secret> }}
    webhook-type: webhook-trigger
    payload: |
      blocks:
        - type: "section"
          text:
            type: "mrkdwn"
            text: "<a Block Kit mrkdwn string>"

Job has timeout-minutes: 5.

Expected result:

On v3.0.5: the step completes in ~1–2s and the message is posted once.

Actual result:

On v4.0.0:

• The same message is delivered to Slack multiple times (usually 5 copies per run).
• The step logs its resolved inputs and then produces no further output until the job is cancelled at the timeout — roughly 4+ minutes of silence.

We did not change retries; the logs show the default retries: 5 in both versions.

07:00:01Z  ##[group]Run slackapi/slack-github-action@<v4 sha>
07:00:01Z    webhook: ***
07:00:01Z    webhook-type: webhook-trigger
07:00:01Z    errors: false
07:00:01Z    retries: 5
07:00:01Z  ##[endgroup]
           (no output for ~4m20s)
07:04:21Z  ##[error]The operation was canceled.

(The job started at 06:59:17Z; the cancellation at 07:04:21Z matches timeout-minutes: 5.)

Attachments:

Example failed runs

• https://github.com/camunda/camunda/actions/runs/29898638740
• https://github.com/camunda/camunda/actions/runs/29808797086 (source of the timeline below)

Start by reproducing the supplied workflow step with slackapi/slack-github-action at v4.0.0, using webhook-type: webhook-trigger and the five-minute job timeout, then compare it with v3.0.5. Trace the action entry point after inputs are resolved, focusing on retries and webhook delivery; done means v4 completes within seconds and posts exactly one message.