> Portal Navigation:
> 
> - Append `.md` to any URL under `https://dev.wix.com/docs/` to get its markdown version.
> - Pages are either content pages (article or reference text) or menu pages (a list of links to child pages).
> - To get a menu page, truncate any URL to a parent path and append `.md` (e.g. `https://dev.wix.com/docs/sdk.md`, `https://dev.wix.com/docs/sdk/core-modules.md`).
> - Top-level index of all portals: https://dev.wix.com/docs/llms.txt
> - Full concatenated docs: https://dev.wix.com/docs/llms-full.txt

## Resource: Service Plugins

## Namespace: ecom-additional-fees

## Article: Introduction

## Article Link: https://dev.wix.com/docs/velo/events-service-plugins/e-commerce/service-plugins/ecom-additional-fees/introduction.md

## Article Content:

# Introduction
The Additional Fees service plugin (formerly SPI) is a service provider interface that allows site owners and collaborators to add additional fee calculations that don't come 
natively with Wix to their site. The service plugin allows you to change how apps, such as Wix Stores and Wix Bookings, calculate charges during checkout. Additional fees are calculated and 
seen in all eCommerce platform pages including cart, checkout, orders, and payments. Examples of additional fees are surcharges based on customer location, special 
handling during shipping, or gift wrapping.

Wix eCommerce calls the service plugin endpoint [`calculateAdditionalFees()`](https://www.wix.com/velo/reference/spis/wix-ecom/ecom-additional-fees/calculateadditionalfees) to 
retrieve the relevant data for a site collaborator to add additional fees. Collaborators can then implement their own logic to calculate additional fees, and return 
the calculated fee data in the structure provided by Wix eCommerce.

Note that `currency` in the [`calculateAdditionalFees`](https://www.wix.com/velo/reference/spis/wix-ecom/ecom-additional-fees/calculateadditionalfees) response must match 
your site's currency. You can find the currency of your site using the [`getPaymentCurrency()`](https://www.wix.com/velo/reference/wix-site-backend/generalinfo-obj/getpaymentcurrency)
function.

Learn more:
 + [Velo: Custom App Extensions Using Service Plugins](https://support.wix.com/en/article/velo-custom-business-app-extensions-using-spis-beta)
 + [Additional Fees Service Plugin](https://support.wix.com/en/article/velo-tutorial-ecommerce-additional-fees-custom-extension)

### To add a service plugin
1. [Add the plugin to your site](https://dev.wix.com/docs/develop-websites/articles/coding-with-velo/integrations/custom-extensions-spis/custom-app-extensions-using-sp-is.md#step-1-create-a-new-extension-on-your-wix-site).
2. Update the [`getConfig()`](https://www.wix.com/velo/reference/spis/wix-ecom/ecom-additional-fees/getconfig) function in the **-config.js** file that is added to your site during step 1.
3. Update the [`calculateAdditionalFees()`](https://www.wix.com/velo/reference/spis/wix-ecom/ecom-additional-fees/calculateadditionalfees) function in the **.js** file that is added to your site during step 1.