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You included the snippet swatch.liquid with the name of a product option — 'Size' — that does not belong to your product.
'Size'
Use {% include 'swatch' with 'name of your product option here' %}
{% include 'swatch' with 'name of your product option here' %}
Example: {% include 'swatch' with 'Color' %}
{% include 'swatch' with 'Color' %}
This is case-sensitive! Do not put in 'color' if your product option name is 'Color'.
'color'
'Color'
