We switched servers and just copied over our cs-cart files and db.
We just noticed that now some ajax on the checkout page doesn’t work.
It seems to be ignoring the parameters on the posts and sending the default data over again instead of the new data based on the params.
Like if payment method 1 is selected, if payment method 2 is clicked, the ajax data just returns the html for payment method 1 being selected again.
Also if someone types an email for guest checkout, it just keeps bringing it back to step 1 rather than going to the next step.
If we do a fresh install on the new server, it works just fine. So I’m guessing there’s some setting it detects on install for it to work with certain server settings or something like that. But I can’t seem to find what/where the problem is… 
Please help, we are losing many sales.
At first delete the /var/cache/ and /var/compiled/ folders and reload the page.
Tried that, nogo. Everything else on the site works.
I actually just figured out the issue, and it’s really strange. I’d like to know more of a indepth ‘why’ answer if anyone knows.
I compared all the config files and aside from all my mods, there was one very imaginary difference between the stock install I did on the new server and our install.
In our config.local.php the line:
$config[‘db_type’] = ‘mysql’;
In the fresh stock install it was:
$config[‘db_type’] = ‘mysqli’;
That made all the difference. I realize the mysqli interface is newer and rewritten, but why would that make such a difference? Also that everything else on the site seemed to work, aside from changing the payment method on checkout and the guest checkout email…