Build an invoice reminder workflow in n8n with Google Sheets (idempotent, AU GST wording)

Description and use

Automated invoice reminder workflow in n8n with Google Sheets, idempotent stages, AU GST wording, and email testing via local SMTP catcher.

Problem

Automate sending invoice reminders while avoiding duplicate emails and handling AU GST wording.

Outcome

Daily reminders sent idempotently, AU GST wording applied, sheet updated with last_stage_sent and last_sent_date.

Workflow

• Schedule Trigger (daily 9am, workflow timezone set)
• Google Sheets "Get rows"
• Code node (decision logic)
• Send Email (SMTP)
• Google Sheets "Update row" (match on row_number)

Evidence

Schedule Trigger (daily 9am, workflow timezone set) → Google Sheets "Get rows" → Code node (decide) → Send Email (SMTP) → Google Sheets "Update row" (match on row_number).

Source

Send Email v2.1 appends an n8n attribution footer by default. Turn it off under Options.

Source

Test against a local SMTP catcher (e.g. Python aiosmtpd) before touching a real inbox.

Source

If the business is GST-registered: "Tax invoice … Total includes GST of $X", where X = total ÷ 11 rounded to the cent. Otherwise: "Invoice … No GST has been charged".

Source