CRM vs ERP: Which System Owns Which Part of the Customer?

CRM vs ERP: Which System Owns Which Part of the Customer?

A CRM manages the people you sell to and the deals you are working on. An ERP manages what happens once something is sold: orders, stock, purchasing, invoices, payments and the books. The simplest way to keep them apart is the signed deal. Everything before it belongs in the CRM, everything after it in the ERP.

Most small service businesses do not need a full ERP at all. A consultancy or agency with five people usually needs a CRM for the pipeline and an invoicing and bookkeeping tool such as Lexware Office or sevDesk for the money. That pairing is the "small ERP" for a company without stock or production, and it is covered below along with the larger suite question.

Customermates publishes this guide. It is a CRM, not an ERP or accounting software, and it appears below only where it fits.

At a glance

CRM

Contacts, organizations, deals, pipeline stages, conversations and next steps. Used by sales, account management and founders.

ERP

Orders, invoices, payments, stock, purchasing, production and accounting. Used by finance and operations.

Small service business

A CRM plus an invoicing tool usually covers both sides. A full ERP starts to pay off with stock, purchasing or production.

Connecting them

Pick one owner per field, pass a stable ID across, and sync only the few fields the other side needs: customer data out, payment status back.

CRM vs ERP side by side

The two overlap on customer master data. Both systems need the customer's name and address, and that overlap is where duplicates start. The next section fixes it.

Who owns which record

Before you connect anything, write down one owner per record and field. Unclear ownership causes more sync trouble than the connector itself. This split fits a typical small service business:

Two rules keep this stable. First, only one side may change a field; the other side reads it. Second, both systems store each other's ID (CRM organization ID in the ERP, ERP customer number in the CRM), so you never match records by company name. Names change, get abbreviated and get typed twice.

Do you need a CRM, an ERP, or an invoicing tool?

Start from the problem you have today, not from the software category.

A CRM module inside an ERP often covers contacts and simple opportunities. Test it on your real sales week before you rely on it: how a new LinkedIn or WhatsApp conversation gets onto the customer, how a stalled deal is found, and how a colleague takes over an account. Likewise, the customer file in an invoicing tool starts when there is something to bill. It has no pipeline.

One suite or two specialised systems?

An all-in-one suite puts CRM and ERP modules under one vendor. Odoo is a common example for smaller companies: its pricing page offers a free plan with one app and paid plans that include all apps, among them CRM, Sales and Accounting. The Odoo comparison covers how it compares with a dedicated CRM.

Neither is simpler by default. A suite with a CRM module your salespeople avoid produces the same spreadsheets you wanted to get rid of. Two tools without a clear owner per field produce duplicates. Choose the side of the table whose ongoing work you are prepared to own.

Invoicing tools next to a CRM

For German small businesses the "ERP" side is often an invoicing and bookkeeping tool that hands data to the tax advisor. If you came here looking for a lexoffice alternative, the first question is whether the problem is accounting or sales. Switching accounting tools does not fix lost deals, and none of the pricing pages below lists a sales pipeline or deal stages.

Lexoffice is now called Lexware Office, as the Lexware product page states. What matters for a CRM connection is which plan includes the API:

Plans and API tiers were checked on 8 October 2026. Prices change often, so compare them on the linked pages. Two more checks before you switch: ask your tax advisor which export format they need, and confirm the e-invoice formats you must send and receive. Lexware Office, for example, lists ZUGFeRD and XRechnung on all four plans.

If the real gap is sales, keep the accounting tool and add a CRM next to it. The Lexware developer documentation lists endpoints for contacts, invoices, quotations and payments, plus event subscriptions, which is everything the handover below needs.

The handover, step by step

This is the smallest useful connection between a CRM and an invoicing tool or ERP. It is written for Customermates on the CRM side, but the order of steps applies to any pair.

1. Add the fields the handover needs

   On organizations, add a Text custom field "Accounting customer no.". On deals, add a Text field "Invoice no." and a single choice field "Payment status" with the options Open, Partly paid and Paid. Agree that only the integration writes these fields.

2. Pick the trigger

   Subscribe a webhook to record.updated for the Deals list. Update events list every field that moved with its previous and current value, so your integration can act only when the stage changes to Won and ignore every other edit.

3. Create or match the customer

   If the organization has no accounting customer number yet, create the customer through the accounting tool's API and write the returned number back to the organization through the Customermates REST API. If it has one, reuse it. Never match on company name.

4. Create the invoice or order there

   Create a draft invoice, quotation or order in the accounting tool with the deal's services and value. Customermates does not create quotes or invoices itself. Store the document number in "Invoice no." on the deal.

5. Send payment status back

   When the payment changes in the accounting tool (by its event subscription or a nightly poll), update "Payment status" on the deal. A write that changes nothing produces no new Customermates event, so the integration does not loop on its own updates.

6. Check it weekly

   Filter deals in stage Won with an empty "Invoice no." and save that as a personal view. Anything in it is a failed handover. Failed webhook deliveries are listed under Settings › Deliveries and can be re-sent from there.

The integration itself runs outside both systems: a small service of your own, or an n8n workflow that calls the Customermates API. n8n is a separate product you host or subscribe to. For mapping, authentication, idempotency and monitoring in more depth, read the CRM ERP integration guide.

Where Customermates fits, and where it does not

Customermates is an open-source, AI-native CRM for small client-facing teams, built in Germany. On the CRM side of the table above it covers contacts, organizations, deals with configurable stages on a pipeline board, services as deal line items, tasks, custom fields and saved views. Deal stages carry weights, which give a weighted pipeline value. With Pro or higher on Customermates Cloud, email, LinkedIn and WhatsApp conversations sit on the customer in the unified inbox.

For the connection to an ERP or invoicing tool it offers a REST API, 16 webhook event types and an MCP server with 53 tools, listed on the integrations page.

What it does not do:

• It does not create quotes or invoices, record payments, keep a ledger, manage stock or plan production. Those stay in your ERP or invoicing tool.
• It has no ready-made connector for Lexware Office, sevDesk, DATEV or any ERP. You build the handover above with the API, webhooks or n8n.
• Records import and export one list at a time, as XLSX workbooks or JSON. Moving contacts out of an invoicing tool means saving its export as XLSX and importing organizations first, then contacts.
• The unified inbox and Mate, the assistant, exist only on Customermates Cloud. A self-hosted installation is the open-source core with REST, webhooks and MCP.

If you want CRM and accounting under one login and one vendor, an all-in-one suite fits better than Customermates.

A realistic cost for a three-person consultancy on Pro is €87 per month for the CRM with the inbox, plus the accounting tool's own plan with API access. Billing is monthly. Details are on the pricing page.

Frequently asked questions

Third-party details checked on 8 October 2026 against the official pages of Lexware Office, sevDesk, FastBill, Billomat, Odoo, SAP and Salesforce.