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

# Validation

> Field-level validation errors and input element types for form validation

<Warning>
  Primer Checkout Android SDK is currently in **beta** (v3.0.0-beta.4).
  The API is subject to change before the stable release.
</Warning>

Field-level validation errors reported through `PrimerCardFormController.State.fieldErrors`.

## SyncValidationError

```kotlin theme={"dark"}
class SyncValidationError {
    val inputElementType: PrimerInputElementType
    val errorId: String
}
```

| Property           | Type                     | Description                                                   |
| ------------------ | ------------------------ | ------------------------------------------------------------- |
| `inputElementType` | `PrimerInputElementType` | Field that triggered the error                                |
| `errorId`          | `String`                 | Error identifier or message describing the validation failure |

## PrimerInputElementType

```kotlin theme={"dark"}
enum class PrimerInputElementType {
    CARD_NUMBER, EXPIRY_DATE, CVV, CARDHOLDER_NAME,
    COUNTRY_CODE, FIRST_NAME, LAST_NAME,
    ADDRESS_LINE_1, ADDRESS_LINE_2, CITY, STATE, POSTAL_CODE,
}
```

| Value             | Validation                                      |
| ----------------- | ----------------------------------------------- |
| `CARD_NUMBER`     | Luhn check + card network detection             |
| `EXPIRY_DATE`     | MM/YY format, future date                       |
| `CVV`             | Correct length for card network (3 or 4 digits) |
| `CARDHOLDER_NAME` | Non-empty when required                         |
| `COUNTRY_CODE`    | ISO 3166-1 alpha-2                              |
| `FIRST_NAME`      | Non-empty                                       |
| `LAST_NAME`       | Non-empty                                       |
| `ADDRESS_LINE_1`  | Non-empty                                       |
| `ADDRESS_LINE_2`  | Optional                                        |
| `CITY`            | Non-empty                                       |
| `STATE`           | Non-empty                                       |
| `POSTAL_CODE`     | Format varies by country                        |

## Validation timing

Fields validate **on blur** (when the user leaves a field), not while typing.

<Info>
  `isFormValid` updates in real-time as the user types. `fieldErrors` only updates on blur. Use `isFormValid` for submit button state and `fieldErrors` for error messages.
</Info>