---
schema_version: "1"
id: ae6b41987170f7562aebbf38ee6297a24a8735c4cb16b01999954973e1a18860
title: Prerequisites for a Partner or Custom Tax Engine
collection: admin
version: current
locale: en-us
portal_url: https://docs.salesforce.com/admin/current/en-us/ind/264-0-0/billing_tax_configuration_prerequisites.md
canonical_url: https://help.salesforce.com/s/articleView?id=ind.billing_tax_configuration_prerequisites.htm&release=264.0.0&type=5
source_site: help.salesforce.com
content_type: documentation
content_hash: e29d8f73818053008e470c02cb633b5bdd27275433ee25762203b0c866ce200d
description: If you want to calculate taxes by using your own tax engine or by integrating the Billing TaxEngineAdapter Apex interface with a partner app, complete these prerequisites.
products:
  - Revenue Cloud
release: "264"
---
# Prerequisites for a Partner or Custom Tax Engine

If you want to calculate taxes by using your own tax engine or by integrating the Billing TaxEngineAdapter Apex interface with a partner app, complete these prerequisites.

### Required Editions

<table class="slds-table slds-table_bordered slds-max-medium-table_stacked slds-m-bottom_small edition"><colgroup><col></colgroup><tbody><tr class=""><td class="slds-cell-wrap" style="vertical-align:top;">Available in: Lightning Experience</td></tr><tr class=""><td class="slds-cell-wrap" style="vertical-align:top;">Available in: <strong>Enterprise</strong>, <strong>Unlimited</strong>, and <strong>Developer</strong> Editions with <a href="https://help.salesforce.com/s/articleView?id=ind.revenue_licenses_areas_and_features.htm&amp;release=264.0.0&amp;type=5">the Revenue Cloud Advanced license or the Revenue Cloud Billing license</a></td></tr></tbody></table>

## Gather Tax Provider Details

If you want to use a tax service provider, gather this information:

- Tax provider’s seller code
- Tax provider’s mailing address
- Credentials for accessing the tax provider

## Create a Named Credential

After you gather the tax provider details, [create a named credential](https://help.salesforce.com/s/articleView?id=xcloud.nc_named_creds_and_ext_creds.htm&language=en_US) to secure and authenticate API callouts to the tax engine.

## Define a Custom Apex Adapter

If you use your own tax engine, define a custom tax adapter by [extending the TaxEngineAdapter Apex interface](https://developer.salesforce.com/docs/atlas.en-us.revenue_lifecycle_management_dev_guide.meta/revenue_lifecycle_management_dev_guide/billing_tax_engine_adapter_interface_for_standard_tax.htm).

You can model your custom tax adapter’s implementation based on [this example](https://developer.salesforce.com/docs/atlas.en-us.revenue_lifecycle_management_dev_guide.meta/revenue_lifecycle_management_dev_guide/billing_apex_interface_TaxEngineAdapter_Example.htm).

From Summer ’25, Billing supports up to 2000 invoice lines for a single invoice. To avoid limit-related issues, test your TaxEngineAdapter Apex interface’s implementation to make sure that it adheres to the [Apex limit for total heap size](https://developer.salesforce.com/docs/atlas.en-us.salesforce_app_limits_cheatsheet.meta/salesforce_app_limits_cheatsheet/salesforce_app_limits_platform_apexgov.htm).