My courier banding is set up but KCC is still not choosing the correct courier.

The courier bandings table works in conjunction with the On Import Reassess and the On Invoice Reassess options within the Couriers table. It will also be used if your channels are set up to use Courier Groups.

If the reassess option is not enabled, any orders that have been marked to use that courier service will not be reassessed.

If either, or both, reassess options are enabled, any order marked to use a courier service, will be reassessed using the courier bandings table and the most appropriate courier will be selected.

If using Courier Groups within a channel, the re-assess options do not need to be enabled for the couriers within the group.