Overview
Invoice approvals by email create delays and audit trail gaps. Routing approvals through Slack makes the process faster, more visible, and trackable. This setup is ideal for businesses that process vendor invoices and need manager or controller approval before payment.
Before you start
- Slack Pro plan or higher (for Workflow Builder with buttons)
- Accounting tool connected to Zapier (QuickBooks, Xero)
- Zapier Multi-Step plan
- Google Sheet for audit log
Step-by-step guide (4 steps)
Set up the invoice trigger
Connect your accounting tool (QuickBooks, Xero) to Zapier. Trigger: 'New Bill Created' or 'New Expense submitted.' Add a filter: only proceed if amount exceeds your approval threshold (e.g., $500). Below the threshold, auto-approve and record in Slack as FYI only.
Build the Slack approval message
Use Slack's Incoming Webhooks or the Zapier Slack integration to post to your #invoice-approvals channel. Format the message: Vendor: [name] | Amount: $X | Category: [type] | Invoice #: [number] | Due Date: [date] | Submitted by: [person] | Description: [details]. Include a link to the invoice PDF.
Add approve/reject workflow buttons
Use Slack Workflow Builder (Slack Pro+) to add interactive buttons: Approve and Reject. When the approver clicks Approve, a webhook triggers a Zapier action to mark the bill as approved in QuickBooks/Xero and notify the submitter. Reject triggers a message asking for more information.
Use Slack's threaded replies for approval comments. If an approver has questions, they reply in the thread — keeping all context attached to the invoice notification rather than in a separate email chain.
Log all approvals to a Google Sheet
Every approve or reject action triggers a Zapier Zap to log: invoice ID, vendor, amount, approver, approval date, and decision. This creates your approval audit trail — essential for accounting and audits.
What you'll get
Invoice approvals happen in minutes instead of days
Full audit trail of who approved what and when
Approvers have all context in one Slack message — no hunting for invoice PDFs
Below-threshold invoices auto-process without human review
Common mistakes to avoid
Setting the approval threshold too low (everyone spends time approving $20 expenses)
Not logging approvals (no audit trail for accountants or auditors)
Not including the invoice PDF link (approvers can't approve what they can't see)
Frequently asked questions
Do I need coding experience to set up this Slack automation?
No coding is required. This guide walks you through everything using Slack's built-in features and Zapier's visual interface. If you can follow a recipe, you can follow this guide.
How long does this automation take to set up?
Most users complete this setup in 30–60 minutes on their first try. Once set up, it runs completely automatically with zero ongoing effort.
What happens if the automation fails?
Zapier and Make both have error notifications and task history, so you'll know immediately if something goes wrong. We cover troubleshooting steps in the guide above.
Can I customize this automation for my specific business?
Absolutely. The guide includes notes on common customizations. Most automations have multiple variation points — timing, conditions, notification recipients, and more.