1.5.6b PHP 7.3 SiteMapXML v3.9.5

previously reported in sitemap thread but no response

Sitemap(s) not being generated (nothing happens in admin/tools/sitemap when rebuild sitemaps is ticked and send is clicked) - one file shows in files list, sitemap.xml, but it is empty - url domain / sitemap.xml results in 404 - this is error log
Code:
[01-Jul-2019 14:27:12 Australia/Sydney] Request URI: /admin/sitemapxml.php, IP address: 203.63.88.122
#1  require_once(/home/******/public_html/admin/includes/modules/sitemapxml_install.php) called at [/home/******/public_html/admin/sitemapxml.php:21]
--> PHP Warning: Use of undefined constant TABLE_SITEMAPXML_EXTRAURLS - assumed 'TABLE_SITEMAPXML_EXTRAURLS' (this will throw an Error in a future version of PHP) in /home/*****/public_html/admin/includes/modules/sitemapxml_install.php on line 135.
any assistance will be appreciated.

cheers,
Mike