Issue sequential invoice and ticket numbers via webhook and Data Table

Quick Overview

This workflow exposes a POST webhook that issues the next gapless sequential number (for invoices, tickets, or other sequences) by reading and updating a counter stored in an n8n Data Table, and returns a formatted number with an optional prefix and zero padding.

How it works

1. Receives a POST request on a webhook endpoint with a sequence_key and optional prefix and pad parameters.
2. Validates and normalizes the request values, falling back to safe defaults if inputs are missing or malformed.
3. Looks up the matching counter row in the n8n Data Table number_sequences using the provided sequence_key.
4. Calculates the next counter value, applies the requested or stored prefix, and formats the number using the requested zero-padding width.
5. Upserts the updated counter back into the number_sequences Data Table keyed by sequence_key.
6. Returns a JSON response containing the issued formatted number, the updated counter value, and a timestamp.

Setup

1. Create an n8n Data Table named number_sequences with columns sequence_key (string), current_value (number), prefix (string), and updated_at (string).
2. Ensure the Data Table name/reference in the read and upsert steps points to number_sequences and that sequence_key is used as the matching column.
3. Activate the workflow, copy the production webhook URL for /next-number, and configure your calling system to POST a JSON body such as { "sequence_key": "invoice", "prefix": "INV-", "pad": 6 }.
4. If you require strictly no gaps, serialize requests to this endpoint (for example, by ensuring a single caller or limiting concurrent executions) to avoid simultaneous reads of the same counter value.