Website API integrations: stock, accounting, ERP and bookings

en 2026-09-29 6 min read

Connecting the website you already have to a stock, accounting, ERP or booking system through an API is an add-on at EUR 750-2.500, with the quote confirming the scope. Built into a new site, it puts that site at step 04: EUR 3.500-7.500 and 6-12 weeks. Where it lands in either range depends on how many systems are involved, which way the data flows, and how well each system's API is built and documented.

If your site only needs a booking or contact flow, or a CRM's own embeddable form, that is not an API integration: it fits step 03 at EUR 1.500-3.500 in a new build, and booking and smart forms are an add-on at EUR 350-750 on a site you already have.

What an API integration involves

An API is the door another piece of software leaves open so your website can ask it questions or hand it data. Using that door properly takes more than one request:

• Access. Credentials or an authorisation step, set up so the website gets only the rights it needs.
• Mapping. Your stock system's idea of a product, a variant or a VAT rate does not have to match the website's. Every field is matched, and every mismatch needs a decision.
• Direction. Reading data, such as live stock, is one job. Writing data, such as sending an order to accounting, is another. Two-way sync, where both sides can change the same record, is the hardest of the three, because something has to decide which side wins.
• Timing. Ask the other system on every page view, sync on a schedule, or let it notify the site when something changes. Each choice trades freshness against load.
• Limits. An API can cap how many requests it accepts in a period, and the site has to stay inside that cap at busy moments.
• Failure. Any connected system can be slow or down. The site needs to know what to show, what to queue and retry, and who gets told.
• Testing. Against a test environment where the vendor provides one, and with extra care on live data where it does not.

Why an integration is harder than it looks

Once a site is connected, it depends on software it does not control. A broken page shows an error. A broken integration can fail quietly: an order that never reaches accounting, stock shown as available after it has sold, one booking slot offered to two people. The build has to make those failures visible and recoverable, and that is work a page of content never needs. It is why, in a new build, API integrations sit at step 04 alongside logins, dashboards, CRM connections, payments and chatbots.

What sits where on the ladder in a new build

On a site you already have, the step 04 rows are add-ons instead, with the quote confirming the scope: an API or CRM integration at EUR 750-2.500 and payments at EUR 600-1.500. Booking has trade-offs of its own, set out in adding a booking system, and the CRM route is covered in connecting your website to a CRM.

What moves the price

• The number of systems. Each one brings its own access, mapping, limits and failure cases.
• The direction. Read-only is the lightest. Writing needs checks. Two-way sync needs rules for conflicts.
• The API itself. Clear documentation and a test environment make the work predictable. Thin documentation means time spent finding out how the API really behaves.
• How different the data is. If product codes, customer records or tax settings follow different logic in each system, the mapping grows.
• No API at all. Some systems only export files. A scheduled file import can work, but it changes what "live" means, so it is decided during scoping.

What to have ready before scoping

This is the part that waits on you, and having it ready makes scoping faster.

1. The name of each system, and the plan or edition you are on. Check whether that plan includes API access.
2. For each piece of data, which system is the source of truth: stock lives here, prices live there.
3. What should happen on the site when a connected system is down.
4. Who can grant access, at your company or at the vendor, and who can answer questions about how the data is used.

Process and timeline

1. Scoping. Systems, data, directions, source of truth and failure behaviour, plus a read of each API's documentation.
2. A fixed quote in writing, for the add-on or for a new step 04 build.
3. Connections first. Each integration is built and tested against test data before the pages that depend on it.
4. Failure testing. The other system slow, down, or returning something unexpected.
5. Launch and watch. Failed requests are logged, so a problem can be spotted and dealt with.

A new step 04 build runs 6 to 12 weeks. You own the code, the repository and the database. Hosting is agreed per project, and the studio can host. How the builds are made is covered on Next.js development. After launch, Care at EUR 100-300 a month covers updates, monitoring, backups and small fixes. A new connection is a new feature, and is quoted as one.

When to spend less

• The volume is low. If typing a few orders into your accounting software by hand costs you little, keep typing. An integration earns its price when manual entry eats real time or produces mistakes.
• A ready-made connection exists. If the two products you use already offer a connection to each other, switch it on and pay the subscription instead of commissioning one.
• A form or booking flow is enough. A CRM's own embeddable form, or a booking or contact flow with no API behind it, keeps a new build at step 03 and needs no integration add-on on a site you already have.

In the first two cases, do not buy an integration yet, from us or from anyone.

Common questions

What if our system has no API?

There may still be a route: a scheduled file export and import, or a connector the vendor offers. If neither exists, the honest answer can be that the connection is not worth building. Scoping settles which before any quote.

Can you connect to the software we use?

If it has a documented API and you can arrange access, the answer is in that documentation, which is read during scoping. Send the name of the system and the plan you are on with your first message.

What happens when the connected system goes down?

That behaviour is decided during scoping, not discovered at launch. A site can show the last known data, queue what it needs to send and retry later, and notify someone. The aim is that nothing gets lost quietly.

Does an integration need looking after?

Yes. Vendors change and retire versions of their APIs, and a connection has to keep up. Care covers updates, monitoring, backups and small fixes. Reworking a connection for a new API version is quoted when it is more than a small fix, and so is new functionality.

List the systems you want your site to talk to, and we will tell you what connecting them involves. Send them over here.