### [wpforms_process_validate_payment-single](https://wpforms.com/developers/wpforms_process_validate_payment-single/)

**Published:** September 29, 2026
**Author:** Umair Majeed

**Content:**

## Description

The `wpforms_process_validate_payment-single` action fires for each **Single Item** payment field while WPForms validates a submitted form, before any field value is formatted and before the entry is saved.

parametertypedescription`$field_id`string|intField ID as a numeric string.`$field_submit`mixedSubmitted field value (raw data). For this field it is the amount string from the request, or an empty string when nothing was posted for the field.`$form_data`arrayForm data and settings.## More Information

`WPForms_Process::process()` loops over every field in `$form_data['fields']` and calls `do_action( "wpforms_process_validate_{$field_type}", $field_id, $field_submit, $this->form_data )` for each one. This hook is the instance for the `payment-single` field type. It fires on every submission of a form that contains the field, whether or not the visitor filled it in. The file lives in `includes/`, so it fires in Lite and Pro.

This hook is an instance of `do_action( "wpforms_process_validate_{$field_type}", $field_id, $field_submit, $form_data )`. Other instances are `wpforms_process_validate_payment-checkbox` for the **Checkbox Items** field and `wpforms_process_validate_email` for the **Email** field.

The field class registers its own `validate()` on this hook at priority 10 with three arguments. It adds the required-field error. Then, unless the `wpforms_forms_fields_payment_single_field_validate_amount` filter returns false, it checks the amount: a fixed-price item must post an amount equal to the configured price, and a **User Defined** item cannot post a negative amount or an amount below the field’s **Minimum Price** setting.

`$field_submit` is the raw posted string. Run it through `wpforms_sanitize_amount()` before comparing it as a number. To reject the submission, write a message to `wpforms()->obj( 'process' )->errors[ $form_data['id'] ][ $field_id ]`. The `wpforms_process_initial_errors` filter runs on the collected errors after the loop; Conditional Logic uses it to drop errors from hidden fields.

## Source

`wpforms/includes/class-process.php`

## Example

Enforce a minimum amount on a User Defined Single Item field that carries the CSS class set-minimum, and stop the submission with an error under the field when the amount is lower.

```

/**
 * Enforce a minimum amount on a User Defined Single Item field.
 *
 * @link https://wpforms.com/developers/wpforms_process_validate_payment-single/
 *
 * @param string|int $field_id     Field ID.
 * @param mixed      $field_submit Submitted field value (raw data).
 * @param array      $form_data    Form data and settings.
 */
function wpf_dev_process_validate_payment_single( $field_id, $field_submit, $form_data ) {

    // Only run on my form with ID = 143, remember to change this to match your form ID.
    if ( absint( $form_data['id'] ) !== 143 ) {
        return;
    }

    // Only run on fields that have the CSS class "set-minimum" in the field's Advanced tab.
    $classes = explode( ' ', $form_data['fields'][ $field_id ]['css'] ?? '' );

    if ( ! in_array( 'set-minimum', $classes, true ) ) {
        return;
    }

    $minimum_amount = 5;

    if ( (float) wpforms_sanitize_amount( $field_submit ) < $minimum_amount ) {
        wpforms()->obj( 'process' )->errors[ $form_data['id'] ][ $field_id ] = sprintf(
            /* translators: %s - minimum amount. */
            esc_html__( 'Minimum amount is %s.', 'wpforms' ),
            wpforms_format_amount( $minimum_amount, true )
        );
    }
}
add_action( 'wpforms_process_validate_payment-single', 'wpf_dev_process_validate_payment_single', 10, 3 );
```

## Reference Article

- [How to Set Minimum Amount for a Price Field](https://wpforms.com/developers/how-to-set-minimum-amount-for-a-price-field/)

**Categories:** Actions Hooks

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