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

# Onramp Flow

> How to buy USDT with VND using Holdstation Pay.

## Overview

The onramp flow allows users to **buy USDT using VND**. The partner creates a deposit order via the API, presents a QR code to the user, and the user pays through their banking app.

## Sequence Diagram

```mermaid theme={null}
sequenceDiagram
    actor U as User
    participant P as Partner
    participant H as Holdstation Pay
    participant Bank
    participant B as Blockchain

    U->>P: Request to buy USDT
    Note over U, P: Input amount in VND
    P->>+H: POST /partners/orders/deposit
    Note over P, H: Use callback for order state update
    H-->>H: Calculate USDT amount to receive
    H-->>-P: Returns {order + payment info}
    P-->>U: Show QR code from payment_info
    U->>P: Scan QR code using banking app
    U->>Bank: Confirm and transfer
    Bank-->>+H: Notify transfer result
    H-->>H: Verify payment
    H->>-B: Execute transfering USDT
    B->>U: Transfer USDT
```

## Processing States Flow

```mermaid theme={null}
stateDiagram-v2
    state "State -> Completed" as C
    state "State -> Failed" as F
    state "State -> Closed" as CL
    state "Fiat Pending = 10" as FP
    state "Fiat Confirmed = 11" as FC
    state "Fiat Failed = 12" as FF
    state "Crypto Pending = 13" as CP
    state "Crypto Confirmed = 14" as CC
    state "Crypto Failed = 15" as CF

    [*] --> FP
    FP --> FC: Bank notify successful result
    FP --> CL: Order expired or closed manually
    FP --> FF: Bank notify failure result
    FF --> F
    FC --> CP: Transfer USDT
    CP --> CC: Transfer successful
    CC --> C
    CP --> CF: Failed to transfer
    CF --> F
    F --> [*]
    C --> [*]
    CL --> [*]
```

## Step-by-Step

<Steps>
  <Step title="Create a deposit order">
    Call `POST /partners/orders/deposit` with the amount in VND, recipient wallet address, token address, chain ID, and callback URL.
  </Step>

  <Step title="Present payment to user">
    Use the `pay_data` from the response to display a QR code to the user. The QR code contains bank transfer details.
  </Step>

  <Step title="User completes payment">
    The user scans the QR code with their banking app and confirms the VND transfer.
  </Step>

  <Step title="Receive webhook updates">
    Holdstation Pay verifies the fiat payment and initiates the on-chain USDT transfer. Your callback URL receives status updates throughout the process.
  </Step>

  <Step title="USDT delivered">
    Once the blockchain transfer is confirmed, the order state moves to **Completed** and the user receives USDT in their wallet.
  </Step>
</Steps>