How do I make one weight or price bracket free in my shipping zone?

Each bracket row has a Free tick box next to its Cost.

1. Go to Plugins → Shipping Zone and click Edit on the zone.
2. On your Weight-based (brackets), Price-based (brackets) or Quantity-based (brackets) method, find the bracket, for example Min kg 0 to Max kg 1.
3. Tick Free. The Cost box greys out.
4. Click Save zone.

Orders that fall in that bracket ship free, and the other brackets keep their costs.