Send Webhooks to Slack

Inbound Slack vs outbound Slack

Slack notification use cases

• Alert on failed webhook deliveries or retry exhaustion.
• Notify finance or support about payment events.
• Send deployment, release, or workflow events from GitHub into an engineering channel.
• Send Shopify order or fulfillment exceptions into an operations channel.
• Escalate high-priority provider events while keeping full delivery logs in FastHook.

Create the Slack destination

Use a bot token that can post in the target channel. Keep one destination per channel or alert workflow.

curl -X POST "https://api.fasthook.io/v1/destinations" \
  -H "Authorization: Bearer fhp_xxx" \
  -H "x-team-id: tm_3b5335b627084a838b" \
  -H "Content-Type: application/json" \
  -d '{
    "name": "Slack incident channel",
    "type": "SLACK",
    "config": {
      "channel": "#incidents",
      "text_template": "Payment failed for {{payload.customer.email}}",
      "blocks_template": "[{\"type\":\"section\",\"text\":{\"type\":\"mrkdwn\",\"text\":\"*Payment failed*\\nCustomer: {{payload.customer.email}}\\nInvoice: {{payload.invoice_id}}\"}}]",
      "auth_type": "SLACK_BOT_TOKEN",
      "auth": {
        "bot_token": "xoxb-your-slack-bot-token"
      },
      "rate_limit": 1,
      "rate_limit_period": "second"
    }
  }'

Shape the Slack message

Slack expects a message JSON body, usually with text and optional blocks. Keep the message compact and link back to the system of record when possible.

{
  "text": "Payment failed for {{payload.customer.email}}",
  "blocks": [
    {
      "type": "section",
      "text": {
        "type": "mrkdwn",
        "text": "*Payment failed*\nCustomer: {{payload.customer.email}}\nInvoice: {{payload.invoice_id}}"
      }
    }
  ]
}

Examples

Route only action-worthy events

• Send failures, approvals, escalations, and review events to Slack.
• Do not send every successful webhook unless the channel is explicitly a log stream.
• Use provider event type, payload severity, environment, or customer tier in filters.
• Use a staging Slack destination with a test channel before replaying production failures.

Debug Slack delivery

• channel_not_found or not_in_channel usually means the channel value is wrong or the bot is not in the channel.
• invalid_auth usually means the Slack bot token is wrong, revoked, or missing permissions.
• A 400 can also mean the rendered Block Kit JSON is not valid for Slack.
• A timeout or 5xx should be retried after Slack or network health recovers.
• Inspect the FastHook attempt response body before editing filters or replaying a batch.

Retries, replay, and delivery logs

Slack can reject messages because of invalid auth, channel membership, malformed Block Kit JSON, rate limits, or temporary API failures. FastHook records each Slack delivery attempt so operators can inspect the response before retrying or replaying.

• Retry temporary Slack failures with backoff.
• Replay important missed notifications after fixing channel or token configuration.
• Keep FastHook logs as the delivery record instead of treating Slack history as the source of truth.
• Use filters so replay does not flood channels with old low-priority events.

Slack channel hygiene

Slack is best for events that need a team to notice or coordinate. It is weak as a durable event archive, so pair it with FastHook request and attempt history instead of treating a channel as the source of truth. Use Google Sheets, object storage, or an internal API when the destination needs durable reporting or automated processing.

Design one destination per channel or workflow. That makes it clear which connection owns which alert, and it lets you pause or throttle a noisy channel without changing unrelated webhook routes.

• Include the provider event type and business object id in every Slack message.
• Add severity or environment fields before routing to incident channels.
• Keep high-cardinality debug payloads out of Slack; link to the system of record instead.
• Use rate limits when replaying old failures into a channel people actively read.