Hi Peggy,
I have my dev store running on PHP 7.2 and CDSEO Pro v2.2.0
You need to download the PHP 7.1+ [Beta] version of CDSEO Pro.
Please see Jon's post here -->
https://forum.x-cart.com/showpost.php?p=409658&postcount=20
I have both PHP 5.6 and PHP 7.2 running at the same time. If you need to also please see
https://forum.x-cart.com/showthread.php?t=76594
Good luck!
Paul