After much trial and error I figured it out. It will import it you create and title the columns the same as the squarespace product export.
So, I had to add about missing columns.
Product ID [Non Editable]
Product Type [Non Editable]
Product Type [Non Editable]
Product Page
Stock
CATEGORIES
Visible
On Sale
Product URL (copy product title and slugify it with dashes)
Weight
Width
Length
Height
Then change these:
Variant sku - change to SKU
Variant price - change to Price
Image URL - change to Hosted Image URLs
IF you are uploading as generic CSV it will give you all of these changes as error codes.
Then for good measure I uploaded as a shopify csv file.