The line_item.title field is required by Shopify when doing an import. If you import an order with a blank title Shopify will reject the order with a response the following response, line_items title can not be blank.

For most users providing and mapping the line_items.title field to a column in your CSV file that contains the title isn't a problem. However, there are situations where the title may not be available. For these situations, you can let Shopify map the title of your line item to the title of your products. To do this, you can simply click the Link product by SKU checkbox in the Custom Configuration section and leave the line_items.title field unchecked.

When you have the Link product by SKU option checked the line_items.title field becomes optional. This way Shopify knows to use the title of your product as the line_items.title. To learn more about how to link your products by SKU click here. Don't forget to map the SKU field when linking your products by their SKU.

There are two things to remember before using this feature.

1. SKUs are case sensitive. This means, the SKU in your CSV file must match the SKU on your product exactly. If the case is incorrect the product will not be found and the title will not be mapped.
2. If the SKU can not be found, the order will not import. The product information will come back empty which means the title field will be blank. Shopify will respond with a line_items title can not be blank error.