API Integration for Business: Options, Costs and Pitfalls

API integration means connecting two systems through their APIs so that data moves between them without anyone retyping it. A signed contract creates an invoice, a new lead lands in your CRM, a payment updates an order. You have three routes: the connector the software vendors already offer, a no-code tool such as Zapier, Make or Microsoft Power Automate, or a custom build. The vendors price the first two, usually as a subscription. A custom build with us starts from £5,000 for two systems and from £12,000 for a business-wide integration, at a fixed price agreed before work starts.

This guide explains the three routes in plain English, what the no-code tools cost, when a custom systems integration is worth paying for, and how CRM and ERP integration usually works. It then covers the pitfalls that break integrations after they go live, each with a source. If a cheaper route does the job, we say so.

Key takeaways

• API integration lets two systems exchange data and trigger each other automatically. It is worth doing when people copy data between systems by hand, or when two systems disagree about the same customer.
• The three routes are a native connector, a no-code tool and a custom build. Start with the cheapest one that does the job, and move up when your logic, volume or access rules outgrow it.
• No-code tools bill by subscription and usage. At the time of writing, Zapier Professional starts from $19.99 a month on yearly billing, Make Core from $9 a month billed annually, and Power Automate Premium is £11.50 per user per month excluding VAT.
• A custom integration with CodeLeap starts from £5,000 for two systems and from £12,000 business-wide, with ongoing support from £400 a month.
• Integrations break after go-live on plan-gated API access, rate limits, retired API versions and errors nobody sees. Plan for them before you build.

What is API integration?

API integration means connecting two or more software systems through their APIs, the published interfaces each system offers to other software, so that data and actions pass between them automatically. One system sends an authenticated request to another, or is notified when something changes, and a tool or a piece of code decides what happens next.

Typical jobs are a form submission that creates a CRM record, a signed contract that raises an invoice, or a new customer in the CRM that appears in your accounts system. You probably need one when someone on your team copies data between systems every day, or when two systems disagree about the same customer.

If you are a developer looking for how to call an API, this guide sits one layer above that: choosing a route, budgeting for it and keeping it working once real data flows through it.

Native, no-code tool or custom: which route fits?

There are three routes, and the cheapest one that does the job is usually the right one. The table shows where each wins and where it stops.

	Native connector	No-code tool (iPaaS)	Custom integration
What it is	A connector one of the vendors built, switched on in the app’s settings or marketplace	A hosted tool such as Zapier, Make or Microsoft Power Automate, where you build workflows from prebuilt connectors	Code written against both systems’ APIs and run for you
Wins when	Both apps already offer a connector that moves the records you need	The trigger and action are simple, both apps have connectors, and someone in-house can maintain it	The logic is unusual, several systems are involved, volume is high, or API access is restricted
Cost shape	Set by each vendor, so check the listing	A subscription that rises with usage	From £5,000 for two systems, then support from £400 a month
Watch for	It syncs what the vendor chose to sync, in the direction the vendor chose	Per-task billing, and a tool that quietly becomes critical infrastructure	Needs a proper build and someone to look after it

Start with the native connector if both apps have one, after checking which records and fields it moves and in which direction. If it covers half of what you need, a no-code tool can fill the gap.

What do Zapier, Make and Power Automate cost?

No-code integration tools charge a subscription that rises with usage. The entry prices on the vendors’ own pages (October 2026) are below. Zapier and Make list US dollars on the pages we read, so convert before you budget. Microsoft lists pounds and says its price does not include VAT.

Tool and plan	Entry price shown	Billing basis	Currency
Zapier Professional	From $19.99 a month	Yearly; $29.99 a month if billed monthly	US dollars
Make Core	$9 a month for 10,000 credits	Billed annually; $10.59 a month if billed monthly	US dollars
Power Automate Premium	£11.50 per user per month	Paid yearly	Pounds, excluding VAT

Three things matter more than the headline price.

Usage drives the bill. Zapier says every step in a Zap uses tasks, and Make counts each module action as one credit. As an illustration with the inputs shown, a Make scenario with three module actions that runs 500 times a month uses 1,500 credits (3 × 500), well inside Core’s 10,000. More flows, retries and a busy month change the plan you need, so estimate the runs before choosing a tier.

Free plans have limits that matter for integrations. Zapier’s Free plan includes 100 tasks a month and two-step Zaps. Multi-step Zaps and webhooks start on Professional. Make’s Free plan allows up to 1,000 credits a month.

The tool becomes part of your infrastructure. Once a Zap or scenario moves invoices or customer records, it needs an owner and a failure alert.

When is a custom API integration worth it?

A custom integration earns its cost when one or more of these is true.

• The logic spans several systems. Branches, calculations, approvals and rules for when a person steps in are awkward in a no-code tool. For energy broker SBU we built an automation layer across Salesforce, an LLM and the client’s email, where an 85% confidence threshold decides what runs automatically and what waits for a person.
• The API is gated or awkward. Some systems restrict API access by plan, as the pitfalls section shows, and a connector cannot work around that.
• Volume would make per-task billing expensive. If a flow moves thousands of records a day, compare the usage price of a no-code tool at that volume with a one-off build plus support from £400 a month.
• You need an audit trail. A custom integration can log every run in your own storage and send only the fields each system needs.
• You want to own it. With us, all code and IP are yours once the work is delivered and paid for, so the integration is not tied to a subscription.

If the job is two popular apps and a simple trigger, a no-code tool is probably the better buy, and we will say so. Our workflow automation guide helps you pick which processes to automate first.

AI assistants use the same plumbing. If you want an assistant to read your CRM or create records, it needs an API behind it, and an MCP server is the standard way to expose that to AI tools. Our plain guide to what an MCP server is explains how it works.

CRM and ERP integration: patterns that hold up

CRM integration and ERP integration are the same problem with different owners. Sales owns one system, finance owns the other, and each treats the customer record as its own. Many UK businesses have an accounting package such as Xero on the finance side rather than a full ERP, and the patterns are the same. Four decisions matter most.

One source of truth per record. Decide which system owns the customer, the deal, the contract and the invoice. Let the other system hold a copy, and never let two systems edit the same field.

One direction first. One-way sync is simple to reason about. Two-way sync needs rules for what happens when both sides change the same record at once, so add it only when someone can state those rules.

Events over polling. A webhook is a message a system sends when something changes. Polling is your integration asking repeatedly whether anything has changed. Xero says webhooks are “the preferred method for getting real-time updates” and that excessive polling is “the most common cause of exceeding limits” (Xero Developer). Its own example is that polling one endpoint every five minutes for one organisation uses 288 calls a day. As an illustration, polling four endpoints that way makes 1,152 calls a day, which is more than the 1,000 a day Xero allows an app on its starter tier.

Shared identifiers. Store each system’s record ID in the other. Matching on names or email addresses is how duplicates start.

Our work for an international events group shows the pattern. We connected Pipedrive, SmartDocs and Xero without replacing any of them. Signature detection updates the CRM. One multi-event agreement is split into separate CRM deals, each with its own value and pipeline stage and traceable to the original contract. Once a contract is signed, the invoice is raised in Xero automatically. We delivered it in three phases. The result is around 500 invoices a month that no longer get typed by hand. These are sales invoices raised from won deals, so the flow runs from CRM to accounts.

How much does a custom API integration cost?

With us, connecting two systems you already use starts from £5,000, and a business-wide integration starts from £12,000. For larger estates with many systems, an integration audit and plan starts from £4,000, and the integration build from £10,000 (see enterprise software integration). Each price is fixed and agreed before work starts, you pay in milestones as each stage is delivered, and you can cancel within the first 21 days for a full refund. After launch, maintenance and support start from £400 a month. Our software development cost guide covers other project types.

What moves the price:

• How many systems and flows. Each extra system multiplies the mappings, the tests and the failure cases.
• How good the APIs are. A well-documented API with webhooks is quicker than one with gated access, no sandbox or limited endpoints.
• Direction and rules. One-way sync is cheaper than two-way sync with conflict rules.
• Volume and reliability. Retries, queues and monitoring take real work, and matter more as volume grows.
• Payments. Taking or reconciling card payments adds security and testing work, so we treat it as its own piece of payment integration.

You will also pay third-party costs: subscriptions for the systems themselves, and any plan or add-on a vendor needs to give you API access. If you are comparing API integration services, ask for four things in writing: which systems and directions are covered, what happens when a call fails, who is alerted, and what the monthly support includes.

What goes wrong with API integrations?

These problems show up after go-live, so plan for them at the start.

API access gated by plan or edition. Salesforce’s REST API guide says API access is enabled by default in Enterprise, Performance, Unlimited and Developer Edition orgs. Professional Edition orgs can add it as an add-on. A request to an org without API access returns an API_DISABLED_FOR_ORG error (Salesforce). The energy broker above ran a Salesforce edition without API access as standard. We negotiated access on its existing plan, so it needed no tier upgrade, and its team kept working inside Salesforce. That guide still uses Salesforce’s older edition names. Salesforce introduced Core, Advanced and Max editions on 3 September 2026 (Salesforce), and the guide does not cover them yet, so check what your edition includes before you commit to a design. Our guide to bespoke CRM covers API access on Salesforce’s small-business editions.

Rate limits. Every API caps how fast you can call it. Xero allows an app 5 concurrent calls and 60 calls a minute per connected organisation. The daily limit is 1,000 calls on Xero’s starter developer tier, where new apps begin, and 5,000 on higher tiers. These tiers belong to the app, not to your Xero subscription plan. Exceed a limit and you get an HTTP 429 response with a Retry-After header (Xero Developer). HubSpot’s limits for privately distributed apps rise by subscription tier, from 100 requests per 10 seconds per app and 250,000 a day per account on Free and Starter to 190 and 1,000,000 on Enterprise. The daily limit is shared across all apps in the same HubSpot account (HubSpot). Build queues and back-off into the integration so a limit slows it down instead of failing it.

Data mapping and duplicates. Two systems rarely agree on what a customer, a company or a “status” means. Write the field mapping down, decide how records are matched, and test with real, messy data. Retries must be safe to repeat, or one network blip creates two invoices.

Errors nobody sees. A sync that fails silently leaves the two systems out of step until someone notices. Log every run, alert a named person on failure, and keep a way to replay a failed message.

Authentication and least privilege. Give each integration its own credentials with only the access it needs, and keep secrets out of code and spreadsheets. If a tool is replaced or a person leaves, you can then revoke one credential without touching the rest.

UK GDPR duties. If an integration or a tool moves personal data on your behalf, its provider is probably your processor. Article 28 of the UK GDPR says a controller shall use only processors “providing sufficient guarantees”, and that a binding contract has the processor act “only on documented instructions” (legislation.gov.uk). The ICO says processors must implement appropriate technical and organisational measures to secure the data (ICO). In practice, send each system only the fields it needs and check the contract with every tool in the chain. This is general information, not legal advice.

Vendor API version deprecations. Vendors retire old API versions. Salesforce commits to supporting each REST API version for a minimum of 3 years from first release. It says it notifies customers who use a version scheduled for deprecation at least 1 year before support ends. Versions 30.0 and earlier are retired, and a request to a retired version returns a 410:GONE error. Versions 31.0 to 40.0 are scheduled to be deprecated and unsupported from Summer ‘27 and retired from Summer ‘28 (Salesforce). An integration nobody has touched in years can stop working with no change on your side, so record which API versions yours calls and diarise the retirement dates.

A sensible next step

The quickest useful step is to name the two systems you want connected and the one flow that costs you the most time, such as a won deal becoming an invoice. From that we can tell you whether a native connector, a no-code tool or a custom build fits.

For two systems or a business-wide integration, start with our systems integration service, from £5,000 and £12,000 respectively. For several systems across a larger business, an integration audit and plan from £4,000 comes first and ends in a costed, sequenced integration plan.