OnBuy Integration: Seller API, Boost Listings & UK-Focused Marketplace Management

About OnBuy: Founding, Investors and Market Position

Founding and Timeline (2016 – Today)

OnBuy was founded in 2016 in Bournemouth, Dorset by Cas Paton, who remains CEO in 2024. The platform launched with an explicit positioning against Amazon's first-party retail model: OnBuy does not sell its own products and does not compete with the sellers on its marketplace. Between 2018 and 2022 OnBuy raised over £35M across Series A and Series B rounds, and by 2024 was valued at roughly £200M.

OnBuy's GMV doubled year-on-year between 2022 and 2024, with the marketplace passing £500M in UK GMV in 2024. Today OnBuy operates 30+ product categories — Electronics, Home, Garden, Beauty, Toys, Auto, Pet, Health — and has publicly announced plans for selective European expansion across 2025-2026, but the core platform remains laser-focused on the UK.

OnBuy Ownership and Investors (2025)

• Cas Paton — Founder and CEO, majority shareholder via OnBuy Group
• OnBuy Group — Parent holding entity headquartered in Bournemouth
• Series A + B institutional investors — £35M+ raised across rounds (private investors and growth funds)
• No single mega-shareholder — OnBuy remains an independent, founder-led business
• Valuation: ~£200M (2024, undisclosed Series C in preparation)

Position in the UK E-Commerce Market

OnBuy is the UK's largest independent marketplace behind Amazon UK and eBay UK. Unlike both, OnBuy does not retail its own products — eliminating the conflict-of-interest that drives many high-volume sellers to seek alternatives. With UK-based customer service, lower commission rates than either of its larger competitors, and onboarding measured in days rather than weeks, OnBuy is increasingly positioned as a strategic diversification channel for established multi-channel sellers.

📥 Official OnBuy Seller Application onbuy.com/gb/sell-on-onbuy — free application, 1–3 business days approval →

OnBuy Sales Volume and Scale (2024-2025 Figures)

OnBuy has been the fastest-growing UK marketplace over the past three years. Gross Merchandise Value (GMV) and order volume have roughly doubled year-on-year between 2022 and 2024, with active shopper growth accelerating after the £35M Series B and the launch of OnBuy Boost.

Year	UK GMV (£)	Active Shoppers	Active Sellers	Categories
2020	~£90M	3M	3.5K	25+
2022	~£250M	6M	5K	28+
2024	~£500M	10M+	8K+	30+
2025 (forecast)	~£750M	13M	11K	32+

This trajectory has been driven by the OnBuy Boost advertising platform, the structural undercutting of eBay/Amazon commission rates, and consistent investment in UK-based customer service — a clear differentiator versus the offshored support models of larger competitors. For UK sellers, adding OnBuy as a third or fourth marketplace is now one of the most cost-effective growth levers available.

Opening an OnBuy Store (2026 Current Rules)

1. Legal and Financial Requirements

To sell on OnBuy you must operate as a registered UK business (sole trader, limited company or partnership). VAT registration is required once you exceed the HMRC threshold (currently £90,000 turnover) and recommended from day one if you plan to scale. Making Tax Digital (MTD) compliance for VAT submissions is mandatory.

• Companies House registration (or HMRC sole trader / UTR)
• VAT number (mandatory above £90K turnover; recommended below)
• UK business bank account — payouts settle here every 14 days
• UK business address — used for seller verification and returns
• UK GDPR / Data Protection Act 2018 registration with the ICO
• Trading Standards compliance — product safety markings (UKCA, CE)
• EPR compliance — Extended Producer Responsibility for packaging

2. Applying to the OnBuy Seller Panel

Applications are submitted via onbuy.com/gb/sell-on-onbuy. Approval is one of the fastest in the UK marketplace landscape — typically 1 to 3 business days (compared with 2-6 weeks for Otto or Zalando). Once approved, OnBuy issues your Seller ID, API key and API secret — these are the three credentials Zunapro needs to bring your storefront live.

3. Listing Rules and Content Standards

OnBuy enforces clear content rules to keep search results consistent across sellers:

• Title: 50-150 characters, brand + product name + key attribute
• Imagery: white background, minimum 1000×1000px, up to 8 images, no watermarks or text overlays
• Description: HTML supported, minimum 200 characters
• Category mapping: OnBuy category ID + attributes (colour, size, material)
• Barcode (GTIN/EAN): strongly recommended — speeds up product matching against the OnBuy catalogue
• Content score: aim for 80+ to surface in browse pages and OnBuy Boost

OnBuy Commission Rates (2026)

OnBuy's commission structure is one of the most competitive in UK e-commerce. Listing fees are free; you only pay a final value fee when an order completes. Rates range from 5% to 9% per category — meaningfully below eBay (typically 12.8%+) and Amazon UK (typically 8-15%+). Sellers who subscribe to OnBuy Boost at £19/month unlock reduced tiers. Below are the three commission bands:

Net margin calculation: Sale price − Final value fee − VAT (20%) − Shipping cost − Product COGS = Net profit. Zunapro's pricing module runs this calculation for every SKU and category, so you never accept a sale below your configured minimum margin.

OnBuy API Integration — Technical Details

The OnBuy Seller API is a RESTful interface that lets sellers synchronise products, stock, prices, orders, shipments and returns with the OnBuy platform programmatically. API base URL: https://api.onbuy.com/v2/. Full reference documentation is published at https://api.onbuy.com/docs.

API Authentication

The OnBuy API uses OAuth 2.0 Client Credentials flow. Your apiKey and apiSecret are exchanged for a short-lived bearer token sent in the Authorization header. Tokens expire roughly every hour; Zunapro handles refresh transparently so your sync never drops.

Core Endpoint Categories

• Products API — create, update and retire listings; map to OnBuy categories; query content score
• Inventory API — synchronise stock levels and prices (bulk endpoint, up to 100 SKUs per request)
• Orders API — list orders, update statuses, generate dispatch packets
• Shipments API — book and print shipping labels, push tracking numbers
• Returns API — process return requests; accept or reject
• Settlements API — reconcile payouts, fees and invoices
• Webhooks — instant callbacks on new orders, status changes and stock events

Rate Limits and Error Handling

OnBuy enforces a rate limit of around 10 requests per second per seller. Exceeding it returns 429 Too Many Requests. Common error codes: 400 (invalid product payload), 401 (auth failure / token expired), 404 (category or barcode not found) and 500 (OnBuy upstream error — retry). Zunapro's integrator applies exponential-backoff retries and a dead-letter queue so transient errors never break a sync run.

OnBuy Boost — Advertising and Subscription Platform

OnBuy Boost is OnBuy's own advertising and subscription product, combining two value propositions: a £19/month subscription that unlocks reduced commission tiers, and a CPC (cost-per-click) advertising platform for promoted placements in search and category browse pages.

Boost Subscription Benefits

• Reduced commission — typically 1-2 percentage points lower across all bands
• Priority dispatch labelling on listings — increases click-through
• Access to seasonal campaigns (Black Friday, Boxing Day, January Sales)
• Enhanced analytics dashboard — competitor pricing benchmarks
• Priority UK-based account management

Boost CPC Advertising

Sponsored placements work on a familiar bid model: you set a maximum cost-per-click, OnBuy auctions placement against competing bidders, and you pay only when a shopper clicks. Typical CPCs range from £0.08 to £0.45 depending on category competitiveness. Zunapro's bid-management module surfaces ROAS by SKU and pauses underperforming campaigns automatically.

OnBuy Fulfilment Model — 3PL and Direct Dispatch

Unlike Amazon's FBA model, OnBuy operates no native fulfilment centres. Sellers fulfil orders from their own warehouse or via a third-party logistics (3PL) partner of their choice. This keeps fixed costs low but means dispatch performance is entirely under your control — and dispatch metrics directly impact your seller score.

Recommended Fulfilment Approaches

• Self-dispatch — best for low-to-medium volume (under 500 orders/month) and bulky/custom items
• 3PL partner — recommended above 500 orders/month; UK 3PLs typically charge £1.50-£3.50 per order pick-pack
• Multi-channel 3PL — share inventory across OnBuy, Amazon UK and eBay UK to optimise stock allocation

Carrier Options (All Integrated)

OnBuy integrates natively with the UK's major carriers, all of which are mapped inside Zunapro's shipping module:

• Royal Mail — Tracked 24/48, Special Delivery, international
• Evri (formerly Hermes) — cost-effective for lightweight parcels
• DPD UK — premium 1-hour delivery slots, ideal for higher-value items
• Yodel — broad UK coverage including rural postcodes

OnBuy Seller Performance Score and Cancellation Rates

OnBuy assigns each seller a performance score from 1 to 10 that directly impacts listing visibility and Boost campaign eligibility. Key factors that drag the score down:

• Cancellation rate — out-of-stock cancellations are the single biggest penalty; above 2% triggers warnings, above 5% risks account suspension
• Late dispatch — orders not dispatched within the stated handling window
• Return rate — outliers vs. category average (fashion typically tolerates 25%+; electronics under 5%)
• Customer reviews — keep your seller rating above 4.0 stars
• Message response time — buyer messages must be answered within 24 hours

Zunapro's real-time stock sync reduces cancellation risk by roughly 90%: the moment a sale clears on your website or any other marketplace, the OnBuy listing is updated within seconds — eliminating oversell.

OnBuy VAT, MTD and HMRC Compliance

UK sellers on OnBuy must comply with HMRC VAT rules. Once turnover exceeds the £90,000 VAT threshold, registration is mandatory; many sellers register voluntarily earlier to reclaim input VAT. Standard VAT is 20%, applied to most product categories. Some categories (children's clothing, books) attract zero-rated VAT and must be configured correctly in your catalogue.

HMRC's Making Tax Digital (MTD) regime requires VAT returns to be submitted via approved software — manual portal entry is no longer permitted for VAT-registered businesses. Manual invoicing also becomes impractical above ~100 orders/day.

Zunapro's UK invoicing module:

• Auto-generates VAT invoices the moment an OnBuy order data feed arrives
• Integrates with Xero, QuickBooks, Sage and FreeAgent for MTD-compliant submission
• Handles return credit notes automatically on refund events
• Produces quarterly VAT100 summaries and EC Sales Lists
• Emails the customer a PDF VAT invoice on dispatch
• Complies with UK GDPR / Data Protection Act 2018 for customer data handling

OnBuy Returns and Customer Service

Under the UK Consumer Contracts Regulations, shoppers have a statutory 14-day cooling-off period from delivery to return most items for a full refund. Fashion typically sees 25-35% return rates, electronics 3-8%, and home/kitchen 8-15%. Poor returns handling damages seller score quickly.

OnBuy's Standard Returns Process:

1. Buyer opens a return request from their OnBuy account (within 14 days of delivery)
2. Seller (you) authorises the return and issues a prepaid return label or a return address
3. Buyer ships the item back via the chosen carrier (Royal Mail / Evri / DPD UK)
4. On receipt and inspection, seller refunds within 3 business days (statutory: 14 days max)
5. OnBuy reflects the refund in the buyer's wallet or original payment method

Zunapro's returns module tracks every stage automatically, raises an in-panel notification for the seller, and issues a credit note invoice — keeping VAT records and Trading Standards documentation aligned.

OnBuy Integration with Zunapro — 4 Steps (10 Minutes)

1. Enter your OnBuy seller credentials — In the Zunapro panel under Marketplace → OnBuy, paste your Seller ID, API key and API secret obtained from the OnBuy seller portal.
2. Connect your existing storefront — Native connectors for Shopify, WooCommerce, Magento, BigCommerce and PrestaShop. Enter your store API URL and access key.
3. Run the category-mapping wizard — Drag-and-drop your storefront categories to OnBuy categories. AI suggestions complete the mapping in minutes.
4. Trigger the first synchronisation — Products, stock, prices, orders and shipping all start syncing automatically. Within 10 minutes your OnBuy storefront is being managed from the Zunapro panel.

OnBuy Integration FAQ