n8n Workflow: FX Card Rate Check with Frankfurter & Slack

Spot FX card rate premiums automatically—then report them to Slack

This n8n workflow checks foreign-currency card charges in your Google Sheets, pulls historical exchange rates from the Frankfurter API, calculates premiums versus expected billed amounts, writes results back to Google Sheets, and posts a clear summary to Slack.

What this workflow does

• Runs monthly (or on-demand): Trigger it on a schedule or manually to keep your FX monitoring up to date.
• Reads your FX statement: It imports charge rows from the “FX statement” tab and identifies entries where the transaction currency differs from your configured base currency.
• Fetches market rates per date range: It builds per-currency date ranges and requests historical exchange rates from the Frankfurter API for the required period.
• Calculates premiums and flags issues: For each charge it computes the effective rate, expected billed amount, premium percentage, and extra amount—then assigns a status such as OK, High premium, Below market, Rate unavailable, or Check data.
• Updates results safely in Google Sheets: It appends or updates rows in the “FX check” tab using a stable row key to avoid duplicates on re-runs.
• Posts a Slack summary: Sends totals, highlights the highest premium charges, and flags rows needing attention—or posts a “nothing to check” message if no foreign-currency rows are found.

Use cases

• Ongoing review of FX premiums on card transactions across multiple currencies.
• Automated reconciliation for SaaS operators who want consistent monthly reporting.
• Operational monitoring to identify “Rate unavailable” or “Check data” items without manual spreadsheet work.

Technical details

• Google Sheets (OAuth2): read from “FX statement” and write to “FX check” tabs.
• Frankfurter API: historical exchange rates used for premium calculations.
• Slack: posts the run summary to your selected channel.
• n8n nodes used: if, set, code, slack, sticky note, http request.