Integrations: Connecting ERP, CRM, and Your Online Store

Interfaces connect ERP, CRM and online store by transferring data automatically from one system to the other – orders, stock levels, customers, invoices. To make this work reliably, you define a leading system for each data type, document the field mapping and choose the right integration approach: direct connection, integration platform or a custom middleware. Error handling and monitoring are part of it from the start.

The store knows the order, the inventory system knows the stock level, the CRM knows the customer and accounting knows the invoice. They just do not talk to each other. So data is retyped, exported, imported and reconciled – every single day. This article explains which data flows are typical in mid-sized companies, which integration approaches exist and what matters for stable operation.

How to tell that interfaces are missing

• Orders from the store are transferred to the ERP by hand.
• The store shows items as available that sold out long ago.
• Customer data exists in three systems – with three different addresses.
• Leads from the website form land in an inbox instead of the CRM.
• For every report, exports are merged in Excel.

Each of these points costs time and creates errors. Together they slow growth: more orders then do not mean more revenue for the same effort, but simply more retyping.

Types of interfaces at a glance

An interface – often called an API – is a defined way for two programs to exchange data. Instead of a person copying information from one screen to another, one system queries the other or automatically sends it a message. Which variant fits depends on what the systems involved offer and how current the data needs to be.

Type	How it works	Timeliness	Typical use
Web API (REST)	one system retrieves data from the other or sends it	on request, near real time	orders, items, customer data
Webhook	the source system reports an event immediately	real time	new order, status change, new lead
File exchange (CSV, XML)	files are exported and imported on a schedule	at the pace of the runs	price lists, stock reconciliation, older systems
EDI	standardized message exchange between business partners	as agreed	orders and delivery notices in trade and industry

If an older system offers no interface, file exports or controlled access to the database are often all that is left. That is feasible but more fragile – testing and monitoring then count twice.

Typical data flows in mid-sized companies

Data type	Leading system	Direction	Timeliness
Item master data and prices	ERP (or PIM)	ERP → store	on change or scheduled
Stock levels	ERP	ERP → store	at short intervals or by event
Orders	store (until handover)	store → ERP	immediately
Customer master data	ERP or CRM, depending on the process	both directions, clearly defined	immediately or at intervals
Leads and inquiries	CRM	website → CRM	immediately
Invoices and payment status	ERP / accounting	ERP → store and CRM	on event
Shipping status	shipping system	shipping → ERP → store and customer	on event

A flow from order to invoice

A customer orders in the store. The order goes straight to the ERP, which reserves the stock and creates the sales order. The warehouse receives the picking order, the shipping system generates the label and the tracking number goes to the customer automatically. As soon as the goods leave the building, the invoice is created, accounting takes over the document and the CRM records the purchase in the customer history. Employees only step in when something deviates from the normal case – for example an item is missing or an address is ambiguous.

Three approaches to integration

Direct connection

Two systems are connected directly, often through a ready-made plugin. This is quick to set up and ideal for simple cases. With many systems, however, you end up with a tangle of individual connections that can cause problems with every update.

Integration platform

Platforms such as n8n or Make connect many services through prebuilt building blocks. They suit manageable workflows and can be adapted quickly. With complex logic, large data volumes or strict data protection requirements, they reach their limits.

Custom integration layer

A purpose-built middleware sits between the systems, translates data, buffers messages and logs every step. It is the most robust approach when business processes depend on the integration – and the basis for connecting further systems later. We implement it as part of our API and backend development.

Criterion	Direct connection	Integration platform	Middleware
Setup	very quick	quick	more effort
Business logic	hardly any	simple to medium	arbitrarily complex
Error handling	mostly rudimentary	retries and alerts possible	freely designable, including an error queue
Adding further systems	difficult	good	very good
Dependency	plugin vendor	platform vendor	low, code and operation in your hands
Best suited for	two systems, standard case	manageable workflows	business-critical, individual processes

Seven ground rules for stable interfaces

1. One leading system per data type: Decide where items, prices, customers or stock levels are “the truth.” They are maintained only there.
2. Document the mapping: Which field corresponds to which? How are units, tax rates, currencies or status values translated?
3. Unique references: Order or customer numbers prevent a repeated transfer from creating a record twice.
4. Plan for failures: Systems are sometimes unreachable. Good interfaces retry transfers automatically, and no data gets lost.
5. Monitor and report: If a transfer fails, the responsible team knows immediately – not only through a customer complaint.
6. Security and data protection: encrypted connections, securely stored credentials, only the necessary permissions and documentation of the data flows.
7. Test and safeguard changes: Check cancellations, partial deliveries and credit notes in a test environment, and plan adjustments for when a system changes its interface.

Factor in e-invoicing, GoBD and data protection

Where invoices and accounting data flow, special requirements apply. Since January 1, 2025, companies in Germany must be able to receive e-invoices in B2B transactions; the obligation to issue them applies in stages from 2027 and 2028. Your ERP and the interfaces to accounting should therefore be able to process structured formats such as XRechnung or ZUGFeRD. For handovers to the tax advisor, an export in DATEV format is often added, see DATEV interface. Documents must be archived in a traceable and unalterable way, as required by the GoBD (Germany’s principles for proper bookkeeping and record-keeping).

On data protection, a data flow between systems counts as processing of personal data. Document which data flows where, conclude data processing agreements with service providers and integration platforms, and set retention limits for logs that contain customer data.

Common mistakes and project flow

Common mistakes in integration projects

• Data quality ignored: Duplicates and inconsistent spellings are automated unchecked – and multiplied.
• No leading system: Two systems overwrite each other.
• Only the normal case tested: Cancellations, partial deliveries or credit notes only show up in live operation.
• No ownership: Nobody feels responsible when a transfer fails.
• No maintenance after launch: System updates change interfaces; without maintenance, workflows quietly break.

How an integration project runs

1. Analysis: record systems, data flows and weak points
2. Concept: define leading systems, mapping, integration approach and error handling
3. Implementation: develop the interface and verify it with test data
4. Parallel run: compare results with the previous process
5. Operation: monitoring, adjustments for system updates and further development

The effort is determined mainly by the number of systems, the quality of their interfaces and the complexity of the business rules. A system with a clean, documented API is connected quickly; a legacy system without an interface can account for the lion’s share of the project. Ongoing upkeep is best regulated in a maintenance contract.

How Nano Concepts can help

We analyze your system landscape and suggest the right integration approach – from a simple plugin to a custom solution. For a B2B wholesale portal with more than 5,000 items, we implemented the connection to the ERP so that the product range and orders work together without duplicate maintenance. In a real estate CRM portal, the onOffice integration ensures that properties and contacts stay in the established industry software and can still be used in the custom portal. Our own comparison portals Tarifemaxx.de and KreditKoala.de show how partner connections and automation work together in continuous operation.

Custom development including backend and API starts with our Professional package from €8,000; after the free initial consultation, you receive a transparent quote. A clean integration is also the foundation for further process automation.

This article does not replace legal advice.