Product must be Ready for Jet in order to be posted. Hover over the red X to reveal the missing required attributes. They must be "Enabled" on the Jet Properties page in order to send the available inventory to Jet.
Listing on Jet Individually
Jet Properties page - Open the action menu and select Post on Jet and Press GO.
Listing in Bulk
Manage Inventory page - Select products and select Launch on Channel and pressing GO. On the next page select Jet from the dropdown and press Continue.