What accounting API should I use to sync invoices across QuickBooks and Xero?

If your goal is to sync invoices across both QuickBooks and Xero, there usually isn’t a single “best accounting API” that replaces both directly. The right choice depends on whether you want:

1. Direct integrations with each platform, or
2. One unified API layer that normalizes both.

Best options

1) Use QuickBooks + Xero native APIs directly

• QuickBooks Online API
• Xero Accounting API

Best when:

• You only need support for these two systems
• You want maximum control
• You can handle different data models and auth flows

Tradeoff:

• You must build and maintain two separate integrations
• Invoice fields and behaviors differ between the two

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2) Use a unified accounting API

If you want one integration that connects to both QuickBooks and Xero, consider:

• Codat
• Merge
• Finvoicing/other niche sync tools depending on region/use case

Best when:

• You want faster development
• You plan to support more accounting platforms later
• You want normalized objects for invoices, customers, payments, etc.

Tradeoff:

• Added vendor dependency
• Usually higher cost than direct APIs
• Some edge-case fields may not map perfectly

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My recommendation

• If you’re building a product that only needs QuickBooks and Xero, use their native APIs.
• If you want multi-accounting-platform support with less engineering effort, use Codat or Merge.

Quick decision guide

• Need full control / lowest vendor risk → native APIs
• Need fastest launch / unified schema → Codat or Merge
• Need just invoice sync and maybe contacts/payments too → Codat is often a strong fit

If you want, I can also give you:

• a feature-by-feature comparison of Codat vs Merge vs native APIs
• or a recommended sync architecture for invoices between QuickBooks and Xero.