Migration Guide

Audience: Engineering teams migrating from the previous Complyt API to the Abacus Tax Engine API Last Updated: February 2026 Migration Support: Available through end of June 2026 - contact your account team

Overview

The Abacus Tax Engine API is a ground-up rebuild of the Tax Engine. The core concepts are the same - customers, exemptions, transactions - but the API contract has been modernised. The changes are consistent and mechanical: once you understand the patterns, the migration is straightforward.

What's the same:

• Authentication approach (client credentials → Bearer token)
• Three core resources: Customers, Exemptions, Transactions
• Upsert semantics (safe to call on every order)
• Tax calculation logic and output

What's changed:

• All field names are snake_case (previously camelCase)
• Upsert endpoints moved from path-based to body-based
• Several fields have been regrouped into logical sub-objects
• The source field is now a named integration enum
• Exemptions have been significantly simplified
• Several Complyt API management endpoints have been removed

At a Glance

1. Authentication

No conceptual change. You exchange client credentials for a short-lived Bearer token and pass it on every request.

Endpoint Change

2. The source Field

In the Complyt API, source was an opaque numeric string ("1" through "15") assigned by Complyt to identify your integration.

In the Abacus Tax Engine API, source is a named enum that identifies the integration platform. Use the value that matches your system:

Use api if you are calling the API directly.

3. Customers

Endpoint Mapping

Upsert Pattern Change

In the Complyt API, source and externalId were URL path parameters. In the Abacus Tax Engine API, they move into the request body.

Complyt API:

PUT /v1/customers/source/3/externalId/CUST-001
Body: { "name": "Acme Corp", ... }

Abacus Tax Engine API:

PUT /v1/customers/
Body: { "source": "api", "external_id": "CUST-001", "name": "Acme Corp", ... }

Field Mapping

Customer Address Change

The Complyt API had a single address object on the customer. The Abacus Tax Engine API separates this into addresses.billing and addresses.shipping.

Complyt API:

{
  "address": {
    "street": "350 Fifth Avenue",
    "city": "New York",
    "state": "NY",
    "zip": "10118",
    "country": "US"
  }
}

Abacus Tax Engine API:

{
  "addresses": {
    "billing": {
      "street": "350 Fifth Avenue",
      "city": "New York",
      "state": "NY",
      "zip": "10118",
      "country": "US"
    },
    "shipping": {
      "street": "350 Fifth Avenue",
      "city": "New York",
      "state": "NY",
      "zip": "10118",
      "country": "US"
    }
  }
}

Both billing and shipping are optional. If you only have one address, populate whichever is relevant.

Customer Type Values

Unchanged:

4. Transactions

This is the most significant change. The request has been reorganised into logical sub-objects.

Endpoint Mapping

Core Field Mapping

Addresses - Structure Change

The Complyt API had shippingAddress and billingAddress at the root. The Abacus Tax Engine API nests all addresses under a single addresses object.

Complyt API:

{
  "shippingAddress": {
    "street": "350 Fifth Avenue",
    "city": "New York",
    "state": "NY",
    "zip": "10118",
    "country": "US"
  },
  "billingAddress": { "..." }
}

Abacus Tax Engine API:

{
  "addresses": {
    "shipping": {
      "street": "350 Fifth Avenue",
      "city": "New York",
      "state": "NY",
      "zip": "10118",
      "country": "US"
    },
    "billing": { "..." },
    "shipping_from": { "..." },
    "supplier": { "..." }
  }
}

shipping_from and supplier are new optional fields. shipping_from is used when origin-based tax rules apply. Both can be safely omitted.

The shipping address in the response includes a matched_address object with the validated, geocoded address used for jurisdiction determination:

Customer Reference - Structure Change

The Complyt API had customerId at the root. The Abacus Tax Engine API moves customer-related fields under customer_details, and adds two new ways to reference a customer:

Complyt API:

{
  "customerId": "7c9e6679-7425-40de-944b-e07fc1f90ae7"
}

Abacus Tax Engine API - option 1: by internal UUID:

{
  "customer_details": {
    "customer_id": "7c9e6679-7425-40de-944b-e07fc1f90ae7"
  }
}

Abacus Tax Engine API - option 2: by external ID:

{
  "customer_details": {
    "customer_external_id": "CUST-001",
    "customer_source": "api"
  }
}

Abacus Tax Engine API - option 3: inline upsert:

{
  "customer_details": {
    "customer": {
      "external_id": "CUST-001",
      "source": "api",
      "name": "Acme Corp",
      "external_created_at": "2024-01-01T00:00:00Z",
      "external_updated_at": "2024-01-01T00:00:00Z"
    }
  }
}

Line Items - Field Mapping

Transaction Status Values

Currency - Structure Change

Complyt API:

{
  "currency": "EUR",
  "refRate": 1.0856
}

Abacus Tax Engine API:

{
  "currency_details": {
    "currency": "EUR",
    "manual_exchange_rate": 1.0856
  }
}

manual_exchange_rate is optional. If omitted, the Abacus Tax Engine API fetches the exchange rate automatically.

Refund Fields - Structure Change

Complyt API:

{
  "isRefundLinked": true,
  "refundLinkedPercentage": 0.5
}

Abacus Tax Engine API:

{
  "refund_info": {
    "is_refund_linked": true,
    "refund_linked_percentage": 0.5
  }
}

refund_linked_percentage is a decimal fraction, not a percentage: 0.5 means 50%, 1.0 means full refund.

Transaction Response Body

The Abacus Tax Engine API returns significantly richer output than the Complyt API. Key new sections:

tax object - the primary field for reading total tax owed:

amounts object - aggregated monetary breakdown:

Per-item response fields (new):

taxability_reason values:

{
  "id": "550e8400-e29b-41d4-a716-446655440000",
  "tenant_id": "7c9e6679-7425-40de-944b-e07fc1f90ae7",
  "external_id": "INV-2024-00456",
  "source": "api",
  "transaction_date": "2024-06-15T14:30:00Z",
  "document_name": "INV-2024-00456",
  "is_tax_inclusive": false,
  "transaction_type": "invoice",
  "transaction_status": "active",
  "created_from": null,
  "external_created_at": "2024-06-15T14:30:00Z",
  "external_updated_at": "2024-06-15T14:30:00Z",
  "created_at": "2024-06-15T14:30:05Z",
  "updated_at": "2024-06-15T14:30:05Z",
  "tax": {
    "total_tax": "8.27",
    "effective_tax_rate": "0.082500"
  },
  "amounts": {
    "total_items_amount": "99.98",
    "taxable_items_amount": "99.98",
    "tangible_items_amount": "99.98",
    "non_taxable_amount": "0.00",
    "final_transaction_amount": "99.98",
    "total_discount": "0.00",
    "transaction_level_discount": "0.00"
  },
  "currency_details": {
    "currency": "USD",
    "manual_exchange_rate": null,
    "exchange_rate_info": null
  },
  "refund_info": {
    "is_refund_linked": null,
    "refund_linked_percentage": null
  },
  "addresses": {
    "billing": {
      "street": "123 Main St", "city": "New York", "state": "NY",
      "zip": "10001", "country": "US"
    },
    "shipping": {
      "street": "350 Fifth Avenue", "city": "New York", "state": "NY",
      "zip": "10118", "country": "US",
      "matched_address": {
        "address": {
          "street": "350 5TH AVE", "city": "NEW YORK", "state": "NY",
          "zip": "10118", "country": "US"
        },
        "latitude": 40.7484,
        "longitude": -73.9967,
        "confidence": 1.0
      }
    },
    "shipping_from": null,
    "supplier": null
  },
  "customer_details": {
    "customer_id": "7c9e6679-7425-40de-944b-e07fc1f90ae7",
    "customer_external_id": "CUST-001",
    "customer_source": "api",
    "customer_type_override": null,
    "customer": { "..." }
  },
  "items": [
    {
      "name": "Bluetooth Headphones",
      "tax_code": "ELECTRONICS",
      "unit_price": "49.99",
      "quantity": "2.0",
      "total_price": "99.98",
      "discount": "0.00",
      "total_price_after_discount": "99.98",
      "relative_transaction_discount": "0.00",
      "tangible_category": "tangible",
      "taxable_category": "taxable",
      "taxability_reason": "standard_rated",
      "is_exempt": false,
      "tax": {
        "total_tax": "8.27",
        "effective_tax_rate": "0.082500"
      },
      "jurisdiction_tax_breakdown": {
        "state": {
          "jurisdiction_type": "state",
          "gross_sales": "99.98",
          "taxable_amount": "99.98",
          "non_taxable_amount": "0.00",
          "tax_rate": "0.062500",
          "tax_due": "6.25"
        },
        "county": {
          "jurisdiction_type": "county",
          "tax_rate": "0.002500",
          "tax_due": "0.25"
        },
        "city": {
          "jurisdiction_type": "city",
          "tax_rate": "0.012500",
          "tax_due": "1.25"
        }
      }
    }
  ],
  "shipping_fee": null
}

Paginated List Responses

The GET /v1/transactions/ and GET /v1/customers/ endpoints return a cursor-paginated response rather than a bare array:

{
  "data": [ ... ],
  "cursors": {
    "after": "eyJpZCI6IjEyMyJ9",
    "before": null,
    "has_next": true,
    "has_previous": false,
    "limit": 20
  }
}

5. Exemptions

Exemptions have been substantially simplified. The nested Complyt API structure has been flattened.

Endpoint Mapping

Field Mapping

Jurisdiction Change

The Complyt API required a single state object plus a separate states array. The Abacus Tax Engine API unifies these into a single jurisdictions string array.

Complyt API (single state):

{
  "exemption": {
    "country": "US",
    "state": { "abbreviation": "CA", "code": "06", "name": "California" }
  },
  "states": []
}

Complyt API (multiple states):

{
  "exemption": { "country": "US", "state": null },
  "states": [
    { "abbreviation": "CA", "code": "06", "name": "California" },
    { "abbreviation": "NY", "code": "36", "name": "New York" }
  ]
}

Abacus Tax Engine API:

{ "country": "US", "jurisdictions": ["CA"] }
{ "country": "US", "jurisdictions": ["CA", "NY", "TX"] }
{ "country": "US", "jurisdictions": [] }

An empty jurisdictions array means the exemption applies to all jurisdictions within the country.

Exemption Type Values

Exemption Status Values

6. Endpoints Removed

These Complyt API endpoints do not exist in the Abacus Tax Engine API. The functionality has been internalised or is no longer needed.

7. Migration Checklist

Work through these steps in order:

Authentication

• Update auth endpoint from POST /v1/token to POST /v1/auth/token
• Rename request fields: clientId → client_id, clientSecret → client_secret
• Update response parsing: accessToken → access_token, expiresIn → expires_in, etc.
• Update base URL to the new URL provided by your account team

Source field

• Replace numeric source values (e.g., "3") with named enum values (e.g., "api", "netsuite")
• Confirm the correct source value with your account team if unsure

Customers

• Move source and externalId from URL path into request body
• Rename fields: externalId → external_id, taxNumber → tax_number, customerType → customer_type, customerStatus → customer_status
• Flatten timestamps: externalTimestamps.createdAt → external_created_at, etc.
• Restructure address: address → addresses.billing and/or addresses.shipping
• Rename complytId → id in stored references
• Update get-by-external-ID calls to new URL format

Transactions

• Move source and externalId from URL path into request body
• Rename all top-level camelCase fields to snake_case
• Restructure addresses: shippingAddress → addresses.shipping, billingAddress → addresses.billing
• Move customer reference: customerId → customer_details.customer_id
• Move currency fields: currency + refRate → currency_details.currency + currency_details.manual_exchange_rate
• Move refund fields: isRefundLinked + refundLinkedPercentage → refund_info.is_refund_linked + refund_info.refund_linked_percentage
• Remove lineAmount from line items
• Remove transactionFilingStatus if used
• Ensure unit_price is included on every line item - it is now required
• Update list-response parsing: read records from data[] and paginate using cursors.after / cursors.has_next
• Update transaction_type enum values: SALE → invoice, RETURN → refund
• Update transaction_status enum values: PENDING → active, COMPLETED → paid, FAILED → cancelled
• Update response parsing: read total tax from tax.total_tax
• Update response parsing: read transaction totals from amounts.*
• Update response parsing: handle new per-item fields (total_price_after_discount, taxable_category, taxability_reason, is_exempt)

Exemptions

• Remove the exemption wrapper object - all fields move to the top level
• Replace state object + states array with jurisdictions string array
• Flatten validationDates: fromDate → start_date, toDate → end_date
• Simplify certificate: certificate.certificateId → certificate_id
• Update exemption_type values: FULLY → full
• Update exemption_status values: ACTIVE → active
• Remove classification and status fields

Housekeeping

• Remove any calls to endpoints that no longer exist
• Test all flows in the staging environment before cutover

8. Abacus Tax Engine API - Endpoint Reference

Auth API

Tax Engine API

Questions?

Reach out to your account team or the Tax Engine migration support channel. Migration support is available through end of June 2026.