"Product with SKU already exists on Jet.com"

This error message means that there is already a listing on Jet with this SKU. Jet does not allow duplicate SKUs. If you are trying to edit an active listing, you will need to follow these steps: 

1. Navigate to Listings-->Active Listings
2. Click into the product details (binocular icon)
3. Make any necessary edits you want to make to the listing 
4. Click the blue "Save" button 
5. Return back to Active Listings-->Select the product(s)-->Click the blue "Submit Revisions" button

If you would like to update listings in bulk, here is a guide on how to bulk update your active listings: 

Bulk Listing Updates