bp_notifications_action_mark_unread()

function bp_notifications_action_mark_unread() {

	// Bail if not the read screen.
	if ( ! bp_is_notifications_component() || ! bp_is_current_action( 'read' ) ) {
		return false;
	}

	// Get the action.
	$action = !empty( $_GET['action']          ) ? $_GET['action']          : '';
	$nonce  = !empty( $_GET['_wpnonce']        ) ? $_GET['_wpnonce']        : '';
	$id     = !empty( $_GET['notification_id'] ) ? $_GET['notification_id'] : '';

	// Bail if no action or no ID.
	if ( ( 'unread' !== $action ) || empty( $id ) || empty( $nonce ) ) {
		return false;
	}

	// Check the nonce and mark the notification.
	if ( bp_verify_nonce_request( 'bp_notification_mark_unread_' . $id ) && bp_notifications_mark_notification( $id, true ) ) {
		bp_core_add_message( __( 'Notification successfully marked unread.',       'buddyboss' )          );
	} else {
		bp_core_add_message( __( 'There was a problem marking that notification.', 'buddyboss' ), 'error' );
	}

	// Redirect.
	bp_core_redirect( bp_displayed_user_domain() . bp_get_notifications_slug() . '/read/' );
}