Add a terms and conditions checkbox to the Leaky Paywall registration form.

terms-conditions.php

<?php

// add fields to registration form
add_action('leaky_paywall_after_password_registration_field', 'endo_custom_tos_registration_fields', 100, 2);
function endo_custom_tos_registration_fields($level_id, $level)
{

    // do not show on free levels
    if ( $level['price'] == 0 ) {
        return;
    }

    // adjust wording if the level is recurring
    if ( $level['recurring'] == 'on' ) {
        $text = 'I understand I will be automatically billed on my renewal date unless I cancel';
    } else {
        $text = 'I understand this is a one-time payment that does not autorenew';
    }

?>

    <div class="form-row">
        <input style="display: inline;" type="checkbox" required id="tos" name="tos"> <label for="tos" style="display: inline;"><?php echo $text; ?>, and I agree to all <a target="_blank" href="<?php echo home_url('subscription-terms'); ?>">terms and conditions</a>.</label>
    </div>
<?php

}

add_filter('leaky_paywall_account_setup_validation', 'endo_validate_tos', 20, 2);

function endo_validate_tos($errors, $fields)
{


    if (!isset($fields['tos'])) {
        $errors['tos'] = array(
            'message' => __('You must agree to the terms and conditions to continue.', 'leaky-paywall'),
        );
    }

    return $errors;
}