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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.

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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. pre-auth-flow 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.