Send overdue invoice payment reminders with iFirma, Gmail, PostGrid and Slack

by Łukasz ✓ · 79 views · created 2026-03-25 · Invoice Processing

What this workflow does

This workflow has 41 nodes and runs on a schedule (every 24 hours). Along the way it connects Slack and Gmail. It also calls api.postgrid.com over HTTP.

How it runs

Trigger: On a schedule (every 24 hours).

1. Configuration (Edit Fields (Set)): sets 5 fields: Email/Login, API Key Invoice, X days before due date…
2. Your Company Details (Edit Fields (Set)): sets 11 fields: Company Name, Email, Phone…
3. URL to Fetch Invoices (Edit Fields (Set)): sets 2 fields: url, requestBody
4. Encode API Key (Code): runs custom JavaScript code
5. Fetch Invoices from System (HTTP Request): calls an HTTP API
6. Contains Error? (If): checks a condition and branches into true / false
7. Error Fetching Invoices (Stop and Error): stops the run with an error
8. Extract Invoices (Split Out): splits a list into separate items
9. Filter: keeps only the items that match a condition
10. Assign Endpoint to Invoice Type (Code): runs custom JavaScript code

…plus 30 more steps. See the full node list below.

Services it uses

SlackGmail

HTTP calls to: api.postgrid.com

Before you upgrade to n8n 3.0

Nodes used (12)

• Coden8n-nodes-base.code
• Edit Fields (Set)n8n-nodes-base.set
• HTTP Requestn8n-nodes-base.httpRequest
• Filtern8n-nodes-base.filter
• Stop and Errorn8n-nodes-base.stopAndError
• Ifn8n-nodes-base.if
• Remove Duplicatesn8n-nodes-base.removeDuplicates
• Split Outn8n-nodes-base.splitOut
• Schedule Triggern8n-nodes-base.scheduleTrigger
• Slackn8n-nodes-base.slack
• Gmailn8n-nodes-base.gmail
• Mergen8n-nodes-base.merge

From the author

Overdue Invoice Payment Reminder Workflow Documentation What Is This? This workflow is an automated invoice payment tracking and reminder system for the Polish accounting service iFirma.pl. It monitors unpaid and overdue invoices, then automatically sends…

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