Wait, usually you use line_item.product.metafields.namespace.key to fetch the metafield and line_item.product.metafields.namespace.key**.value** to retrieve its value. Or bin_location is a namespace and value is a key?
Or you’ve simply forgotten either namespace or key?
If value is not a key, but metafield property, after looking at https://help.shopify.com/en/manual/orders/printing-orders/shopify-order-printer/liquid-variables-and-filters-reference#metafield i think maybe you should remove it from your code.