n8n Webhook Workflow: Sequential Invoice & Ticket Numbers

Generate gapless sequential invoice & ticket numbers via an n8n POST webhook

This n8n Webhook Workflow: Sequential Invoice & Ticket Numbers issues the next gapless sequential number on demand. It reads and updates a counter in an n8n Data Table, then returns a properly formatted number (optional prefix + zero padding) as a JSON response.

What this workflow does

When you call the workflow with a POST request, it:

• Accepts a request on the webhook endpoint with a required sequence_key, plus optional prefix and pad parameters.
• Validates and normalizes inputs, applying safe defaults when values are missing or malformed.
• Looks up the matching counter row in the n8n Data Table number_sequences using sequence_key.
• Calculates the next counter value, applies the requested (or stored) prefix, and formats the output using the requested zero-padding width.
• Upserts the updated counter back into the number_sequences Data Table keyed by sequence_key.
• Returns a JSON response including:
  • the issued formatted number,
  • the updated counter value, and
  • a timestamp.

Use cases

• SaaS billing: generate invoice numbers that are consistent and sequential across your system.
• Support operations: assign ticket numbers in a gapless order for every new request.
• Multi-sequence systems: use different sequence_key values (e.g., invoice, ticket) with the same webhook.

Technical details

• Webhook (POST) endpoint exposed by n8n
• Data Table named number_sequences with columns: sequence_key, current_value, prefix, updated_at
• Code node for validation, incrementing, and formatting logic
• Respond to Webhook to return JSON (formatted number, counter, timestamp)
• Sticky Note for workflow documentation

Ideal for automation engineers and n8n users who need reliable, sequential numbering without manual tracking.