ERP Integration for SMEs: Options, Costs and What Usually Breaks

ERP integration means connecting the system that holds your orders, stock and accounts to the other tools around it, so that data is entered once and moves by itself. For most small and mid-sized businesses there are three routes: a connector app, an integration platform such as Make or Zapier, or custom middleware built on the vendors’ APIs. The cheapest route that handles your volume and rules is the right one. When the logic spans several systems, a custom build usually costs less than the workarounds.

This guide is for an SME whose orders, stock and invoices are retyped between an ERP or accounting system, a shop, a warehouse system and a CRM. It covers what the work involves, the systems involved, how the three routes compare, what breaks after go-live and how to phase a project. We offer enterprise software integration, so where a connector app does the job, we will say so.

Key takeaways

• Start with the cheapest route that fits. A marketplace connector app suits a standard flow, an integration platform suits simple links, and custom middleware suits multi-system logic, high volume or approvals.
• Most ERP and accounting systems publish APIs, so the real questions are field mapping, record matching and what happens when a call fails.
• The usual breakages are mismatched fields, duplicates after retries, partial failures, rate limits and vendor API changes. Monitoring and safe retries are the answer.
• A system with no API can often still be reached, through a database connection, a file export or a wrapper.
• With us, an integration audit and plan starts from £4,000 and an integration build from £10,000, with support from £400 a month.

What does ERP integration mean for an SME?

It means one place where each fact is entered, and automatic copies everywhere else. An ERP such as SAP, Dynamics 365 Business Central or NetSuite holds the orders, stock and financial records. In smaller firms the same role is often played by accounting software such as Sage, Xero or QuickBooks.

Around it sit the systems that create the data: a shop (Shopify, WooCommerce, Amazon, eBay), a warehouse or inventory tool (Linnworks, Unleashed, Cin7) and a CRM (Salesforce, HubSpot, Pipedrive). Without integration, people carry data between them. An order lands in Shopify, someone keys it into the accounts, someone else updates stock, and a third person tells the CRM.

At SME scale the first project is rarely “integrate everything”. It is one flow that costs real hours, such as an order creating an invoice, or a won deal raising a purchase order. Our guide to API integration covers the general method, and the Xero integration guide goes deeper on the accounting end.

Which systems usually need connecting?

Start from where the money events happen and work outwards. We work with the systems below. For most of them our public evidence is that we integrate with them, and the shipped work is named further down.

Group	Examples	Role
ERP and finance	SAP, Business Central, NetSuite, Sage, Xero, QuickBooks	Orders, stock, accounts
Shops	Shopify, Woo­Commerce, Amazon, eBay	Where orders arrive
Stock and CRM	Linnworks, Unleashed, Cin7, Salesforce, HubSpot, Pipedrive	Stock, despatch, sales

Each vendor publishes an API, and it is worth reading what yours allows before choosing a route.

• Business Central. Microsoft’s documentation says Connect apps are typically built on standard REST APIs and that the APIs are enabled by default for Business Central online. It also says that adding fields to the standard APIs is not currently possible, so a custom field means a custom API (Microsoft Learn).
• NetSuite. Oracle describes its REST web services as an integration channel that extends SuiteTalk, with a REST-based interface for working with NetSuite records (Oracle).
• Shopify. Shopify documents a GraphQL Admin API for reading and changing store data (Shopify).
• Amazon. Amazon publishes a Selling Partner API for developers building applications for sellers (Amazon).

None of this means the integration is quick. An API gives you access to records, and the work is deciding what each field means and what to do when two systems disagree.

Which route fits: connector, platform or custom?

There are three routes, and they suit different jobs. Here is how they compare.

Route	Fits when	Watch for
Connector app	A standard flow, both sides listed	Fixed behaviour
Platform	Simple triggers, modest volume	Per-run billing
Custom code	Many systems, rules, approvals	Build cost, upkeep

Marketplace connector apps

Many ERPs and accounting systems have their own app stores, and many shops have app listings that sync orders to accounting. A listed app that moves the right records in the right direction is the cheapest route by a distance. Check which records it syncs, in which direction, what it does on failure and whether it handles your tax and product set-up. If any answer is “no” for something you need, move up a route.

Integration platforms

Make, Zapier, n8n and Microsoft Power Automate connect apps through visual workflows. They suit a simple trigger and action at modest volume, and they are quick to start. Their pricing and limits differ, and we compare them in n8n vs Zapier vs Make. The trade-offs come with scale: usage-based billing climbs with volume, audit history can be limited on lower plans, and a complicated multi-step flow becomes hard to read. Where one of them does the job at lower cost than a build, we will say so, and simple links get built on Zapier or Make when that is genuinely cheaper.

Custom middleware

Custom middleware is code that sits between your systems, talks to each through its API and applies your rules. It earns its cost when the logic spans several systems, when approvals or an audit trail matter, when volume makes metered pricing costly, or when a system has no usable connector.

Our work for an international events group shows the pattern. Sales ran in Pipedrive, contracts in SmartDocs and invoicing in Xero, and every handover was manual. We built the integration layer that was missing: signature detection, automatic splitting of a multi-event agreement into separate CRM deals, automatic invoice creation and cross-system field mapping, delivered in three phases. You can read the full account in the events group case study. It extended the systems they already used rather than replacing any of them.

We have also integrated a client’s own platforms behind a product. Connect by CoCentric is integrated with CoCentric’s own identity and HR systems, and Cicerone’s in-app purchases tie into a Shopify store hub. For SBU, an energy business, we built an automation layer across Salesforce, with Companies House data enrichment. SAP, Dynamics 365, NetSuite, Sage, QuickBooks, Linnworks, Unleashed, Cin7 and HubSpot are systems we work with, and we are not pointing to a named case for each of them.

What usually breaks?

Integrations rarely fail on day one. They fail weeks later, on a case nobody tested. Five problems cause most of the damage.

Field mapping. Two systems rarely agree on what a customer, a status or a price means. A “paid” order in the shop may be “awaiting payment” in the ERP. Write the mapping down, field by field, and test it with real, untidy data rather than clean samples.

Matching records. Match on a stored ID, never on a name or an email address. When a record is created in one system, save its ID in the other. Matching on names is how duplicate customers start.

Partial failures and duplicates. A sync can create the invoice and then fail before it updates the order. Retry carelessly and you get two invoices. The answer is a property called idempotency, which in plain words means that doing the same thing twice has the same effect as doing it once. In practice, the integration records what it has already done and checks before it acts, so a retry after a network blip changes nothing.

Rate limits. Every API limits how fast you can call it. Shopify’s documentation says that when a request bucket fills you get a throttle error and have to wait, that your code should stop making requests until enough time has passed, and that the recommended backoff time is one second (Shopify). An integration should slow down and retry automatically, so a busy sales day does not turn into missing orders.

Vendor API changes. Vendors add fields, retire versions and change plan rules. Under our support, which typically starts from £400 a month, an integration is monitored so a breaking change becomes an alert to us rather than missing invoices three weeks later. For the plan-gating and version-retirement examples, see our API integration guide.

Behind all five sits one habit: log every run, alert a named person on failure and keep a way to replay a failed message.

What if the system has no API?

Usually it can stay. Older ERPs and bespoke in-house tools often have no API, but the data is still reachable. There are three ways in, in order of preference:

1. A direct database connection, read-only where possible, which gets data out without touching the application.
2. A scheduled file export, such as a nightly CSV that the integration picks up and validates.
3. A wrapper, a small service that puts a modern API in front of the old system so newer tools can use it.

Wrapping what works is usually cheaper and safer than a rewrite, and our legacy systems guide sets out when to leave a system alone and when to replace it. Where a system genuinely is better replaced, we will show you the numbers for both paths. Be wary of any option that writes straight into an unsupported database, because it can skip the checks the application normally makes.

How should an ERP integration project be phased?

Do it in phases, each of which pays back on its own. The events group work above was delivered in three phases, prioritising the automations with the greatest effect on the team’s workload and expanding from there.

A sensible sequence for most SMEs:

1. Map and cost. List every system, the flows between them and the hours re-keying takes. Identify API limits and legacy constraints before design.
2. Prove one flow. Pick the highest-cost flow, such as order to invoice, and run it with monitoring on a small slice of real data.
3. Add flows. Extend to stock, returns and the CRM one at a time, with the same checks.
4. Hand over. Documentation your team can maintain, alerts to a named owner and a support arrangement for vendor changes.

What does it cost with us?

Two of our services cover this, and the right one depends on the size of the estate.

For named ERP, CRM and legacy platforms, enterprise software integration has two fixed-scope steps. An integration audit and plan starts from £4,000 and maps your application estate, costs the re-keying in hours, identifies API and legacy constraints and ends in a costed, sequenced plan, with no obligation to build. An integration build starts from £10,000 and covers connecting your ERP, CRM and finance systems, wrapping legacy systems with modern APIs, and failures that are monitored and retried automatically. All code and IP are yours on payment.

For SME tool stacks, systems integration starts from £5,000 for two systems connected and from £12,000 for a business-wide integration, with support from £400 a month after go-live. Our AI and process automation work covers the automation that sits on top, such as reading an invoice or sorting an email under human review.

Third-party costs are separate: the systems’ own subscriptions, and any plan or edition a vendor needs for API access.

A sensible next step

Name the two systems that cause the most retyping and the one flow that costs the most hours. From that we can tell you whether a connector app, an integration platform or a custom build fits, and roughly what each route would cost.

For an estate with an ERP, a CRM and a shop, an integration audit and plan from £4,000 comes first. It ends in a costed plan whether or not you ask us to build it.