In order to make Exact Online work it is essential that you configure your catalogue in Shopify in a way that you always have an unique SKU. The SKU is the `code` field that we use in Exact Online. So it is very important that this number is unique per Product Variant to keep your system clean.
These fields are mandatory for Exact Online. Within Shopify it is not mandatory, but Exact Online needs it. Otherwise order processing will throw errors.