I've been able to reach the last checkout page before the thankyou/confirmation page, but can't Place Order due to the following error:

Transaction subsidiary X is not valid for location A. Please choose a different location.

X and A are not the real Location and Subsidiary record names, but you get the idea. I see that the Subsidiary the Web Store is operating under is different from the Default Location for Sales Orders set in Accounting Preferences, but I also don't see any options in Website Setup or SuiteCommerce Configuration to set the default differently for Sales Orders created in the webstore. Do you think this error is about the location on Sales Orders? UPDATE: Changing Accounting Preferences > Order Management > Default Sales Order Location to blank solved the problem. That didn't work until I invalidated the web store cache, cleared the browser's cookies and data, logged out of the web store, logged back into the web store. I made a User Event script on beforeLoad to set the Location to one compatible with the web store's Subsidary, but the value it was setting kept getting overridden default one after it set it to a specific compatible value. I tried setting the Default Sales Order Location back to the original one it had that isn't compatible with the web store Subsidiary, and repeated the web store cache invalidation and browser cache/data clearing, and somehow it still allows the user to Place Order again even after I've put it back the way it was when it didn't allow the user to Place Order due to Location incompatibility with the subsidiary, and it's not overwriting the value the script sets anymore either. Yay! Yay, but an unsettling mystery why it still works.