Foxycart no longer working
Installation and Configuration
I wrote to Foxycart and got this advice below back. If I am correct then the problem is on the Jamroom side.
Are you still supporting the module and have you made changes that broke it?
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It looks like the issue is coming from the custom shipping javascript that is included on the "cart include" template for your store. It is taking care of setting the shipping costs on the checkout, and it looks for options on the product for international shipping and domestic shipping. It then parses the value as "float" and sets it as the shipping cost.
For that example product you provided, there is no product options for domestic and international shipping, so when the javascript tries to parse the value as float, it returns as not being a number (or "NaN").
If your approach for custom shipping costs expects those product options to be present, you'll need to ensure you're passing them with the product and that should correct the issue.
I also can't cache my template from the Foxycart admin panel because it apparently can no longer be found - https://indiegospel.net/foxycart/remote_templates/checkout
It does appear that that URL no longer works. If you have a different URL for your checkout template, you'll need to cache that URL instead.