Invalid date range format in attribute: sale price effective date

Hi,

Thanks for using our plugin and reaching out to us.

First of all you need to make sure you have this field mapping in place:
https://www.dropbox.com/s/t51c9kzlyxv50hb/sale_price_eff_date.png?dl=0

And make sure that for your products that are on sale you set both a start and end data: https://www.dropbox.com/s/4gnxpj8m0ntxm35/sale_price_date.png?dl=0

I had a brief look at your feed and it seems you only set an end date?