# Second Party Prefill API

The Second-Party Prefill API enables Engine partners to **securely pre-populate customer application data** (including PII such as Name, Address, SSN, and Income) into Engine's embedded application consume experience. 

You send the consumer's data server-to-server, receive a short-lived `prefillToken` plus the markup needed to render the experience, and then load that experience for the consumer. The personally identifiable information (PII) never travels through the browser.

{% hint style="info" %}
If you want to pass **full** data prefill with consents programmatically, use Engine's[ **Offer Wall API**](/developer-center/hybrid-api-integrations/offer-wall-api-integrations.md) instead — it provides a more seamless end-to-end experience for that use case. 

The Prefill API is built primarily for partial prefill into Engine's hosted Partner Pages and embedded experiences.
{% endhint %}

## Key Benefits

This integration reduces consumer friction, eliminates data entry fatigue, and **significantly improves conversion rates.**

* **Better UX:** consumers start the application with their information already filled in.
* **Security:** PII is exchanged server-side, so it is never exposed in browser URLs, query parameters, or static HTML.
  * The PII you send is encrypted at rest; the `prefillToken` is an opaque, short-lived reference that Engine exchanges for that data when the experience renders.
  * There are limitations on the number of times a token can be used (`maxUses` is 3) and how long it's valid for (`expiresInSeconds` is 180)
* **Flexible:** supports partial prefill; any field you omit is simply collected from the consumer in-flow.

### Works Across Product Marketplaces

This guide is split by product category because the accepted request fields and the embed markup differ between them. Start with the page that matches your product:

* [**Personal Loans, SLR, & ALR**](/developer-center/hybrid-api-integrations/second-party-prefill-api/loans-marketplaces.md) for Engine's lending experiences (including Personal Loans, Student Loan Refinance, Auto Loan Refinance).
* [**Credit Cards**](/developer-center/hybrid-api-integrations/second-party-prefill-api/credit-cards-marketplace.md) for Engine's credit card marketplace.

The rest of this page covers the parts that are the same regardless of product: how the flow works, authentication, the token lifecycle, your frontend options, and best practices.

## How it Works

{% stepper %}
{% step %}

## Submit User Data

Your server sends the consumer's lead data (PII, financial info, etc.) to the Prefill API.
{% endstep %}

{% step %}

## Receive a `prefillToken`

Engine validates the request and returns a short-lived `prefillToken` plus a destination `partnerPageUrl` and an `embedSnippet`.
{% endstep %}

{% step %}

## Initiate the Frontend User Experience

You either load the embed snippet on your own site or redirect the consumer to the returned partner page URL. Both are returned in every response — you choose which to render.
{% endstep %}

{% step %}

## Consumer Completes Form

The consumer lands on the application with their data prefilled and enters any required fields you didn't send.
{% endstep %}

{% step %}

## Consumer Reviews and Submits Form

The consumer reviews the data, provides consent, and submits to receive prequalified offers.
{% endstep %}
{% endstepper %}


---

# Agent Instructions
This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com.

## Querying This Documentation
If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://even-financial.gitbook.io/developer-center/hybrid-api-integrations/second-party-prefill-api.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.