Case Study
How a Custom Shopify-ERP Integration Eliminated Stock Discrepancies for a UK Retailer
A real-time bidirectional sync between Shopify and a legacy warehouse ERP — eliminating 12 monthly oversells, lifting inventory accuracy to 99.8% and cutting order processing from 4 hours to 40 minutes.
0
Oversells per month (was 12)
99.8%
Inventory accuracy
40 min
Order processing (was 4 hrs)
The challenge
12 oversells per month — and peak season was 8 weeks away
The client was running a Shopify store alongside a legacy ERP system in their warehouse. Because the two systems weren't connected, stock levels were updated manually every morning by a member of the warehouse team.
Between updates, Shopify was selling stock that had already been committed to wholesale orders in the ERP — averaging 12 oversell incidents per month. Each oversell required manual cancellation, customer communication and a refund, costing roughly £85 in admin time and lost goodwill per incident.
How it works
Inside the build
01
Map every stock movement
Audited each path stock could move along — wholesale orders, returns, transfers — so no edge case was missed by the integration.
02
Build real-time inventory push
Used Shopify's GraphQL Admin API to push updates from the ERP into Shopify within 60 seconds of any stock movement.
03
Build webhook-based order push
Shopify orders push back to the ERP instantly on placement via a custom webhook, so warehouse staff see new orders in their picking system immediately.
04
Audit log + failure alerts
All sync events logged to Supabase. Any failed sync triggers an immediate email alert so issues are caught before they become customer-facing.
Benefits
What the business actually gains
0 oversells
Down from 12 incidents per month — eliminating a recurring source of refunds and bad reviews.
99.8% accuracy
Inventory accuracy improved from approximately 94% to 99.8% across both systems.
45 min/day saved
Daily manual stock update task eliminated entirely — every morning, every warehouse.
4 hrs → 40 min
Order processing time reduced as orders now appear in the ERP picking system instantly.
Zero stock complaints
Peak season traded without a single stock-related customer complaint.
ROI in month 1
Return on investment achieved within the first month of operation.
Features
Everything the platform delivers
- Real-time bidirectional Shopify ⇄ ERP sync (≤60s latency)
- GraphQL Admin API for high-volume inventory queries
- Custom webhook pipeline for instant order push
- Per-event Supabase audit log with status indicators
- Email failure alerts with full error context
- Peak-season ready: stress tested for 10× normal volume
Technology
Built on a modern stack
Why it matters
This is what bespoke automation looks like
Two takeaways from this build.
1. GraphQL beat REST for this workload. Inventory queries needed to be granular and high-volume; the GraphQL Admin API let us request exactly the fields we needed and stay well inside Shopify's rate limits.
2. The audit log earned its keep on day one. Within hours of going live, the log surfaced an edge case in the ERP's wholesale order flow we'd never have spotted in testing. Fixed in 30 minutes — no customers affected.
"We went into Black Friday genuinely calm for the first time in years. Stock was right, orders flowed, no awkward refund emails. The system just works."
— E-commerce Manager, UK Homeware Retailer (anonymised)
Services used
Want the same on your site?
FAQ
Frequently asked questions
Will this work with my ERP?
Almost certainly. If your ERP exposes any kind of API or database access, we can build a sync. We've integrated with NetSuite, Xero, Sage, custom in-house ERPs and several niche warehouse systems.
How fast is 'real-time'?
Stock movements propagate within 60 seconds. Orders appear in the ERP within seconds of placement on Shopify.
What if a sync fails?
Every event is logged. Any failure triggers an email alert with the full error context, and the system retries automatically with exponential backoff.
How long does this take to build?
Typically four to six weeks for a single-channel sync. Multi-warehouse or multi-channel setups can take eight to twelve weeks.
Ready to automate your business?
This is just one example of what's possible. If you have a repetitive process costing you time, we can build a custom tool to handle it.
Book a free callMore case studies
How We Eliminated 40 Hours of Weekly Admin for a UK E-Commerce Business
A custom AI workflow automation system that cut a £2.5M UK retailer's manual admin from 40 hours to 3 hours per week — saving roughly £26,000 per year and eliminating data entry errors entirely.
How a Custom Integration API Replaced a Failing Zapier Stack for a UK B2B SaaS
A bespoke event-driven API layer connecting a UK B2B SaaS to HubSpot, Xero and Slack — lifting event delivery from 94% to 100%, saving £18,400 a year in Zapier fees and reconciliation, and paying back in the second month.
How Automated Keyword-Driven Content Updates Increased Organic Traffic by 187% in 6 Months
A B2B services firm connected to SerpAPI via our automated AI CMS — lifting organic traffic 187%, ranking keywords from 23 to 91 in the top 10, and reducing content update labour from 16 hours/month to zero.
Automating E-Commerce Product Data Collection for UK Businesses
A bespoke web application built by Streamline Digital that scrapes, enriches, and exports product data from 15+ e-commerce platforms — saving businesses up to 30 hours of manual work every week.
How a Custom Quotation Platform Cut Bournemouth Removal Quotes from Hours to Minutes
Inside the bespoke quotation system powering manandvanbournemouth.uk — an instant online quote form, AI Smart Intake, live PDF builder and itemised pricing that delivers a transparent, branded quote within minutes of any enquiry.
How We Built Our Own Growth Engine: The Streamline Digital Internal Platform
A single integrated platform — CMS, blog generation, backlink manager, LinkedIn automation, SERP and keyword intelligence, competitor analysis and lead capture — that runs this entire website with about fifteen minutes of human attention a week.
Inside the Admin Console We Built to Run Our Own Agency
Streamline Digital built a bespoke internal admin console that consolidates lead capture, CRM, SEO monitoring, blog automation, LinkedIn scheduling, and backlink outreach into one platform. It replaced approximately eight separate SaaS subscriptions and now runs the agency's entire marketing operation with minimal human oversight.
Related services & guides
Hand-picked next steps from across our guides and services.
- Service
Shopify API integration services
This service directly addresses the core topic of custom Shopify ERP integration mentioned in the case study.
- Guide
custom Shopify app development
The case study discusses a custom integration, which often involves custom app development for Shopify.
- Guide
multi-channel inventory sync
The case study specifically highlights eliminating overselling and achieving high inventory accuracy through integration, directly related to multi-channel inventory sync.
- Guide
custom automation solutions
The ERP integration itself is a form of custom automation solution to streamline business processes.
- Guide
Shopify Integration & API Architecture
This pillar guide covers the broader topic of Shopify integrations and API architecture, providing more context to the case study.