I found a work around for the 412 error previously mentioned. It just didn't like it when there was a - (dash) in the title of the product, so I manually remove the dash in the seo keyword section of the admin product page. Usually I just let it self generate.
However, now I've added products they keep going to THE PAGE YOU REQUESTED CANNOT BE FOUND! as the URL says this:
domainname.com.au/index.php?_route_=category-name/product-name
It only works if I manually change the URL to read like the seo url should domainname.com.au/product-name.
Or if I turn off SEO urls it all works fine, but I would rather have them working.
I have contacted my host, and they directed me to go back to the developer. I have also tried turning off mod-security and it doesn't appear to make a difference.
I double checked the .htaccess, and it all appears good, when I compare it to the .htaccess in 1.2.16 ..
Are there other files I should check?
Could I have accidentally stuffed something up - I've changed a couple of minor details in a couple of .tpl files, and otherwise only changed things in the stylesheet.
The version of PHP I had was a bit low, I had it set at 7.1. I've set it at 7.3 which is the minimum for 1.3.2 although I have higher options. Since the 1.2.16 site is working and hosted on the same account I am cautious about changing things the sites share.
As mentioned previously, the 1.2.16 version I use on a different domain has SEO urls working perfectly, with the same host. It also doesn't care if there is a dash in the title, I usually just use the 'generate seo' option for this reason.
I would love to get them working - not just for the SEO advantage, but because I think they look more professional.