Prestashop and Thirtybees always show free shipping
Setting up the carrier in a new website, the carrier show all teh time the text "Free shipping" and no carrier were available.
Check shipping location and ranges if they are correct setup
Check "out-of-range" behavior is set to apply the cost of the highest defined range, otherwise the carrier is disabled.
Check if the products has the advanced stock management functionality enabled. In case that is really needed
Associate a carrier with a warehouse: Stock > Warehouse >
associate a product with a warehouse: Catalog > Product > Warehouse