Whether you’re building expense tracking, cash flow forecasting, or credit scoring tools, fintech startups often need to connect to customers’ accounting data in platforms like QuickBooks, Xero, FreshBooks, and dozens more.

But each of these integrations comes with its own APIs, authentication methods, data formats, and quirks, which makes building and maintaining multiple platform integrations a time sink. Each new connection needs weeks of engineering work, and after it's developed, you need to keep an eye out for API changes and fix bugs as they appear. As your integration list grows, technical debt also keeps up, which slows down your go-to-market plan and drains resources from your core product.

This is where a unified API can help. Instead of having to grapple with dozens of disparate APIs, it offers a single, consistent interface to connect with several accounting platforms at once.

In this article, you'll learn why this approach is the most efficient and scalable option for fintechs, how it reduces engineering overhead, speeds up time-to-market, and improves performance. You'll also learn why Apideck stands out as the ideal Unified API for accounting integrations.

The Cost of Building Point-to-Point Integrations

In the early days of developing your product, integrating with one or two accounting platforms might feel manageable. You pick a popular option like QuickBooks or Xero, dive into the API docs, and wire up the connection.

But soon, customer requests start piling in:

• "Do you support FreshBooks?"
• "Can I connect my Sage account?"
• "What about Clear Books or Zoho Books?"

For each new integration, your team must study a new API, figure out authentication, map data fields to your schema, and build error handling for edge cases. Multiply that by a dozen or more platforms, and the complexity grows exponentially.

Maintenance is just as demanding. Accounting platforms frequently update their APIs, change data structures, or deprecate versions/endpoints. You need to monitor each integration, test for compatibility, and patch code to prevent downtime. Even small changes, like a field name update, can trigger bugs and support tickets.

On top of this, every integration behaves slightly differently. Some provide real-time webhooks while others require scheduled polling. Data formats vary, which makes normalization a repetitive and error-prone task.

All of this results in fragmented customer experiences, added engineering backlogs, and fewer resources for building the features that differentiate your core product.

The Case for a Unified API

Instead of building separate integrations for QuickBooks, Xero, FreshBooks, and every other platform, you only need to connect to a unified API once to gain access to all the solutions it integrates with. The unified API handles the complexity of authentication, data standardization, and ongoing updates for you.

Simplified Auth

Every accounting platform implements authorization a little differently, from token exchange URLs to refresh token lifetimes. Some require additional scopes for certain data, while others enforce multi-step consent flows.

Normally, your engineers would have to implement, test, and maintain each one separately. A unified API abstracts all of this into a single, consistent OAuth process. Your app interacts with one standardized flow, while platform-specific quirks are handled behind the scenes.

Data Standardization across Platforms

Accounting data is notoriously inconsistent between providers. What one platform calls a customer, another calls client and a third contact. Field names, data types, and even currency formats can vary wildly.

A unified API maps all of these into a consistent schema so that you can query customer once and get reliable, normalized data regardless of the underlying source. This eliminates platform-specific conditionals, reduces mapping errors, and keeps reporting consistent across all integrations.

Automatic API Updates

When a provider changes an endpoint, adds new required fields, or deprecates an old version, the unified API layer absorbs those changes. Your application keeps talking to the same standardized endpoints, so you don't have to refactor your code every time an upstream change happens.

This shields your engineering team from the constant churn of versioning updates, authentication tweaks, or schema changes, all of which are common in the accounting platform space.

Comparing Direct Integrations with a Unified API

Let's walk through a quick example to visualize the value that a unified API adds.

If you were to query "customers" (or "clients"/"contacts") from three major platforms (QuickBooks, Xero, and FreshBooks), here's what the API requests would look like.

For QuickBooks Online, you must include a realmId in the URL, retrieved and stored during OAuth, and use their proprietary query language rather than a standard REST endpoint:

const res = await fetch(
  `https://quickbooks.api.intuit.com/v3/company/${realmId}/query?query=select * from Customer maxresults 50`,
  {
    headers: {
      Authorization: `Bearer ${accessToken}`,
      Accept: 'application/json',
      'Content-Type': 'text/plain'
    }
  }
);
const data = await res.json();

For Xero, every request must include an xero-tenant-id header. Getting this is an extra OAuth step, where you need to list tenants and select the right one. The entity here is called a Contact, which may represent customers or suppliers, so filtering is required:

const res = await fetch('https://api.xero.com/api.xro/2.0/Contacts', {
  headers: {
    Authorization: `Bearer ${accessToken}`,
    'xero-tenant-id': tenantId,
    Accept: 'application/json'
  }
});
const data = await res.json();

On top of that, Xero’s pagination and date formats differ from QBO’s, adding more divergence.

With FreshBooks, the pattern changes again. Here, you must provide an accountId in the URL, which is obtained via a separate API call after authentication, and the endpoint is for clients, not customers or contacts:

const res = await fetch(
  `https://api.freshbooks.com/accounting/account/${accountId}/users/clients`,
  {
    headers: {
      Authorization: `Bearer ${accessToken}`,
      Accept: 'application/json'
    }
  }
);
const data = await res.json();

Field names change once more (organization instead of DisplayName or Name), and the available accounting-specific fields are fewer than in QBO or Xero, which can make analytics or reporting inconsistent.

A unified API replaces all this complexity with a single, consistent interface. Let's look at how it works with Apideck's accounting API, which offers integrations to more than twenty popular accounting solutions.

To fetch customers from one specific platform, you send the same request structure and headers every time:

const res = await fetch('https://unify.apideck.com/accounting/customers', {
  headers: {
    'x-apideck-app-id': process.env.APIDECK_APP_ID,
    'x-apideck-consumer-id': 'consumer_123',
    'x-apideck-service-id': 'quickbooks', // or 'xero', 'freshbooks'
    Authorization: `Bearer ${process.env.APIDECK_API_KEY}`
  }
});
const customers = await res.json();

Or, to fetch from all connected accounting platforms at once, you simply leave out the service ID:

const res = await fetch('https://unify.apideck.com/accounting/customers', {
  headers: {
    'x-apideck-app-id': process.env.APIDECK_APP_ID,
    'x-apideck-consumer-id': 'consumer_123',
    Authorization: `Bearer ${process.env.APIDECK_API_KEY}`
  }
});
const { data } = await res.json();

// Each record includes source service information:
{
  id: 'cust_123',
  name: 'Acme LLC',
  service: 'xero',
  email: 'ap@acme.com',
}

The result is a single normalized customer schema, clear metadata showing the source platform, and no need to reimplement OAuth or data mapping for each provider.

The Benefits of Using a Unified API

The benefits of using a unified API compound quickly:

• Faster development: Adding just one integration unlocks all available platforms, cutting time-to-market from months to days.
• Simplified maintenance: API changes are absorbed at the unified API layer, reducing the need for constant internal patching.
• Consistent customer experience: Standardized data from all platforms ensures all users see the same features and reports regardless of their accounting platform.

The faster you can launch integrations your customers need, the faster you can win deals, retain users, and capture market share.

Instead of hiring more engineers or diverting your existing team to build more than a dozen separate connections, you only integrate once to access every supported accounting platform. This cuts development time and the long-term cost of maintenance.

The most important result is less technical debt. Your codebase remains lean and free from dozens of custom API implementations that become harder to maintain as your team grows.

Choosing the Right Unified API

The right unified API solution should balance speed, security, and flexibility, without adding unnecessary complexity. These factors directly impact how quickly your team can ship, how well your data stays protected, and how easily your systems can adapt to new business needs.

Here is how Apideck balances these requirements:

• No-data-storage approach for stronger security: Apideck acts as a passthrough, never storing your customers' accounting data. This minimizes data liability, reduces compliance overhead, and gives your users peace of mind that their sensitive financial information isn't being warehoused by a third party.

• Flexible pricing built for your needs: Apideck gives you the choice between usage-based billing and customer-based pricing. Usage-based billing lets early-stage fintechs scale integrations in line with growth, avoiding high fixed costs during the MVP or adoption phase. For teams that prefer to forecast based on active customer count, our customer-based model offers a simple, transparent way to plan ahead without penalties for multi-integration use.

• Multi-vertical and global coverage: With coverage for 20+ accounting platforms across multiple regions, Apideck ensures your product can serve a global customer base.

And while this article focuses on accounting integrations, Apideck also offers unified APIs for HRIS, CRM, and other verticals, allowing you to expand your integration strategy without adding new vendors.

• Developer-friendly implementation: Apideck's accounting API provides clean, well-documented endpoints and SDKs in multiple languages. Moreover, it implements a uniform API design to access information from all 20+ platforms.

Conclusion

For fintech startups, integrating with multiple accounting platforms is a necessary evil. The traditional point-to-point approach is slow and costly to build and maintain. Each new integration eats into your engineering bandwidth, delays your go-to-market, and adds to a growing pile of technical debt.

A unified API like Apideck lets you integrate once to get secure, real-time access to 20+ accounting platforms, complete with standardized data and consistent authentication flows. You cut months of development time, reduce your maintenance load, and free your engineers to focus on the product innovations that actually move the needle.