Sometimes a product is added to your catalog and it was created with just one option (i.e. size).
For example, you have one shirt that comes in three sizes. It may have been added to Shopify with just an option for size. Then later you get the same shirt in a different color and you want to add it to the existing product. But since the original product does not have a color option when shopify attempts to add it it does not have a place for the color option and the integration would get an error and no WEB ID would be created for the item.
So, to remedy this, you would have to add a color option to the product in Shopify.
From your Shopify admin, go to Products.
Click the name of the product that you want to edit.
In the Variants section, click Edit options. Make any edits that you need:
To add a new option, click Add another option and enter the option name and a default option value. The default option value will be applied to all the existing variants. You can have a maximum of three options for a product.
To change an option name, click it and enter the new name.
To delete an option value, click the x beside it. Any variants with that option value will also be deleted.
To delete an option, remove all but one of the option values, then click the trash can icon beside the option. When there is only one option, you can't remove it by editing the options. If you want to sell a product without any variants, then you need to delete all the variants.
You can also edit the order of options:
In the Variants section of the product details page, click Reorder variants:
In the Reorder variants and options dialog, click and drag an option name to move it to a different position: