Custom Shopify App Built for a UK Manufacturing Business

Off-the-shelf Shopify apps solve 80% of problems elegantly. The remaining 20% — especially in manufacturing and industrial supply — often require bespoke solutions. This UK manufacturer of specialist fixings and fasteners had a unique challenge: 1,200 trade customers each with negotiated pricing tiers, real-time stock levels that changed hourly, and a legacy ERP system that had been running the business for 15 years.

The Problem We Were Solving

• Trade customers needed to see their individually negotiated prices, not standard RRP.
• Stock levels in Shopify were always out of date — the ERP was the single source of truth.
• Account managers needed to create and send custom quotes directly within the Shopify admin.
• Customers needed the ability to order against their negotiated credit terms without paying at checkout.

The Architecture We Built

We built a private Shopify app using the Shopify Admin API and App Proxy. The app had two components: a webhook-driven ERP sync running every 15 minutes to update stock levels across 8,000 SKUs, and a customer-facing pricing layer that intercepted the cart and checkout to apply account-specific pricing from the ERP's price list data.

The Quote Builder

Account managers needed to generate formal PDF quotes from within the Shopify admin. We built a custom Shopify App Extension embedding a quote builder in the admin sidebar. Managers could select products, apply custom line-item pricing, set validity periods, and send the quote as a branded PDF. Customers could accept the quote and convert it to an order in one click.

Results

• Order processing time reduced from 48 hours to under 4 hours.
• Stock accuracy on the Shopify store improved from 61% to 97%.
• Accounts receivable improved — 84% of trade orders now paid within agreed terms.
• Account manager productivity increased: each manager now handles 40% more accounts.
• Customer satisfaction with the ordering process scored 4.6 out of 5 in post-launch survey.

Key Technical Considerations

Building a reliable ERP sync required careful attention to Shopify's API rate limits and webhook reliability. We implemented a queue-based update system with retry logic, and built an admin dashboard showing sync health status. The client's IT team can now monitor the integration independently without developer support.