## Check the status of the payment session

This endpoint allows you to check the current status of a payment session. The payment session
goes through several states during its lifecycle:

- `PENDING`: The customer has requested to start the payment flow but hasn't begun yet
- `INITIATED`: You (the merchant) have initiated the payment flow and it's ready for the customer
- `SUCCESSFUL`: Payment completed successfully
- `FAILED`: Payment failed or was declined
- `EXPIRED`: Payment expired before completion

You should poll this endpoint periodically to track the payment progress. We recommend polling
not faster than every 1 second.

## Endpoint signature

```http
POST https://api.reservepay.com/sdk/check-status HTTP/1.1
Content-Type: application/json
Accept: application/json

{
  merchant_id: string,
  installation_id: string,
  payment_session_id: string,
}
```

Returns: string

## Request arguments

### `merchant_id` (string)

**Required**. Your merchant ID that uniquely identifies your account.

### `installation_id` (string)

**Required**. The installation ID for this platform (e.g. your iOS app, Android app, website, or terminal).

### `payment_session_id` (string)

**Required**. The ID of the payment session you want to check the status for. This is returned when selecting a payment method.

## Errors specific to this endpoint

### `NOT_FOUND`

This error occurs when we cannot find the merchant account, installation, or payment session with the IDs provided. Double check that you are using the correct IDs.

## Errors common to all endpoints

### `UNHANDLED_ERROR`

This error occurs when the server encounters an unexpected internal error that it cannot handle gracefully. This typically happens due to bugs, infrastructure issues, or edge cases that weren't anticipated during development.

### `INVALID_ARGUMENTS`

This error occurs when the request contains invalid or missing parameters. Common cases include missing required fields, or values that don't match the expected format or type.

### `BAD_VERSION`

This error occurs when making requests to an API version that is either deprecated or not yet released. This commonly happens when using an outdated SDK or when the API version specified in the request URL is incorrect.