Output nonce, action, and option_page fields for a settings page. Please note that this function must be called inside of the form tag for the options page.
<?php settings_fields( $option_group ) ?>
<?php echo '<form method="post" action="options.php">'; settings_fields( 'my-plugin-settings-group' ); ?>
settings_fields() is located in
This function is part of the Settings_API.