> ## Documentation Index
> Fetch the complete documentation index at: https://devzone.nayax.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Two-Phase Pre-Authorization Flow

> Enable external data collection and manual authorization triggers for fueling sessions.

This guide walks through the **Two-Phase Pre-Authorization** fueling flow. This sequence allows for external data collection (such as plate numbers) after the card is detected but *before* the authorization request is sent, providing a more flexible validation process for fueling sessions.

## Payment flow

Visualize the 2-phase pre-authorization process in the following diagram, which illustrates the separation between card detection, user input, and the final authorization.

<img src="https://mintcdn.com/nayax-44d6e37b/wVLGYVAtRc6gMQRT/images/pre-auth-flow.png?fit=max&auto=format&n=wVLGYVAtRc6gMQRT&q=85&s=f6a4c7bc1cd3768c1c90848863f4e54e" alt="pre-auth-flow" width="955" height="1426" data-path="images/pre-auth-flow.png" />

Below is a breakdown of the sequence:

1. Your system triggers the `cardDetect` command to enable the VPOS reader.
2. Once a card is detected, the VPOS sends a confirmation back to your system.
3. Your system sends a `displayInput` command to the VPOS to prompt the user (e.g., "Enter plate#").
4. The user enters the data on the VPOS terminal, which is sent back to your system as a "user entry".
5. After receiving the required input, your system sends the `authorize` command to the VPOS.
6. The VPOS confirms the card is authorized with an **OK** response.
7. Your system sends a `displayScreen` command to show "Start refuel" to the consumer.
8. The fueling session takes place (**Start refuel → End refuel**).
9. Your system sends the `settle` command to the VPOS to capture the final transaction amount.
10. Your system displays a "Thank you" message and optionally triggers the `print` command for a receipt.