I DL'ed the zip (from: https://www.webassist.com/PowerCMS.zip)
Fresh install at URL and site stated in private area.
Navigated to install_cms folder. Successfully initiated install. No issue Inserting Serial Number
Then delivered with page whose filename is "database.php" that present a 500 error and the message:
"This page isn't working".
ftp credentials and all else also in private area.
(Incidentally, in case it is an issue then the PHP version on this latest site is 7.4, ready to run the latest PowerMessenger that I intend to install here. The PHP version on the site on which I currently have a working version of CMS has only a 5.xx version of PHP, and that site does NOT have a current working version of PowerMessenger_7. I have that on a third domain).