WooCommerce can't see product variations

The problem could be in the product creation process. I can't know for sure without looking at the data used for product creation, but I'll try anyway. I see that you use two different attributes for the variants. So, the products should be created to support those attributes correctly:

{    "name": "Sample Product",    "type": "Example",    "description": "A Demo Product",    "images": {        {            "src": "path/to/img",            "position": 1        }    },    "categories": {        {            "id": 12        }    },    "attributes": {        {            "id": 2,            "name": "Color",            "variation": true,            "visible": true,            "options": [ 'Red', 'Green', 'Blue' ]        },        {            "id": 3,            "name": "Size",            "variation": true,            "visible": true,            "options": [ 'M', 'L', 'XL' ]        }    }}

If "variation": true is missing in the main product's attributes, then the variants created under attributes without that flag won't show up as variants. I know it's a shot in the dark, but maybe it'll help you.