I just purchased 4seo, and it immediately failed on the first configuration option.
It's asking me if the website is public. I answer YES, and get the following message:
Cannot save configuration.There was an error trying to save configuration to the server. Please reload the page or try again later.
Details: View developer tools console for details.
I don't know what the developer tools console is, so that is no help at all.
FYI - The site previously used SH404SEF
Admin login as follows:
https://example.com.au/administrator/
username: example
pw: example