You need to make sure that you have made changes to all 3 files listed , for example in this first file it shows you the folders that you need to enter to find the file that you need to make changes to , copy the code below , enter the file , remove any existing code and just paste the new code and do this for all three files, after you do this it is still going to ask you for your username and purchase code just type in any random letters or numbers ,anything at all the installation will go through successfully
For example here you need to enter the resources folder,in there you'll see the installer folder,in there you'll see the src folder then controllers folder and finally the base controller.php file ,remove any code in there and copy and paste the code just below then save ,do this for all 3 files,good luck
the design and functionality of this script is very beautiful and extensive if you have any issues installing it just post a screenshot of the issue 👍
PS I also noticed that the sub domain you are trying to install the script on does not have SSL installed , so far all of the hosting providers I have used offer free SSL and most of the time they add it to your domain name automatically but they don't always do this with sub domains you will have to do it manually you can do so by searching for the ssl/tls section on the control panel of your hosting , that section should display all the domains and sub domains and give you the option to activate the free SSL that comes with each one