> For the complete documentation index, see [llms.txt](https://docs.blockchain.com/pay/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.blockchain.com/pay/getting-started/customise-the-widget.md).

# Customise the Widget

{% hint style="info" %}
All query parameters used in your integration must be [URL-encoded](https://www.w3schools.com/tags/ref_urlencode.ASP) to ensure they work correctly. For example use `satoshi%40blockchain.com` for email addresses. 
{% endhint %}

## Mandatory Query Parameters

The only parameter you need when loading the widget is the API Key, this links activity in that widget to your account. 

For more ways to customise your widget, see our document on [Optional Customisation](/pay/getting-started/customise-the-widget/optional-customisation.md).

<table><thead><tr><th width="202">Parameter</th><th>Description</th></tr></thead><tbody><tr><td><code>apiKey</code><br><mark style="color:green;">required</mark></td><td>Use this parameter to initiate the widget for your app. This is how we track customer activity to your account and load all your customizations. </td></tr></tbody></table>