Hi,
I see no error when accessing the checkout or cart on your website (with the link you provided as private information that others can't see but we can). And I can see that the debug is not activated, so it doesn't seem to be linked to that.
So it seems to be working fine. Maybe you found the issue already ?
Otherwise, if you have totally blank pages, rather that the "debug", it's the "error reporting" setting that you want to activate to get the error messages on the blank pages.
And if you don't get them when you activate that setting, or if you aren't able to reproduce it, you can check the PHP error log of your server where the "fatal error" messages linked to blank pages are normally logged even when not displayed (you might need to ask your hosting on how to access that log).