Clarification was added to V3 Catalog API on creating products and product variants. Included are examples on how to create a product with variants, adding variant options and use cases for creating variant options.

• Create a Product
• Create a Variant
• Create Variant Options

Create a Product with Variants

{
    "name": "BigCommerce Coffee Mug",
    "price": "10.00",
    "categories":[
            23,21
        ],
        
    "weight": 4,
    "type": "physical",
    "variants":[
        {
            "sku": "SKU-BLU",
            "option_values":[
                    {
                        "option_display_name": "Mug Color",
                        "label": "Blue"
                    }
                ]
        },
        {
            "sku": "SKU-GRAY",
            "option_values":[
                    {
                        "option_display_name": "Mug Color",
                        "label": "Gray"
                    }
                ]
        }
    ]
}