Hi,
In the settings of your module, you've configured the "relation" setting to "in the same category" instead of "related products". So the module will display the products in the same category are the current product, instead of displaying the related products of the current product.
The error "An error has occurred while fetching the JSON data: HTTP 404 status code." doesn't come from HikaShop so I don't know why you have it but I don't think it is related.
Also, make sure that you turn off the caching on your website or you might not see the change after you modify that setting.