To show an accessory product as one product instead of its individual variants, you can create a product template for the accessory product and set it as a configurable product. This way, when you add the accessory product to the main product's invoice or purchase order, it will be displayed as one product with the option to select the desired variant.

To create a product template and set it as a configurable product:

1. Go to the "Inventory" module and select "Products" from the drop-down menu.

2. Click on "Create" and select "Product Template" from the drop-down menu.

3. Enter the product information and set the "Product Type" to "Configurable Product".

4. Save the product template and create the variants for the accessory product.

5. When you add the accessory product to the main product's invoice or purchase order, it will be displayed as one product with the option to select the desired variant.

Additionally, you can set the product as a kit, this way, you can add all the variants of the accessory product in one line.