Did you look up HostGator php version? If HG is already on 8.1 then you will have to upgrade to mysqli with latest files.
I think in the other thread, it was explained how to find your php version.
Two ways to find out what php version you are using:
1) Use cPanel and look for MultiPHP Manager. That will tell you the current version. To change, select the latest one (after you have prepped your WA code!)
2) OR create a new php file with this code:
<?php phpinfo(); ?>
- name it info.php or similar & upload
- go to that page in browser and it will show what version your server is using on that domain