Not able to add zone after manual create new zone type

Summary:

In 'Manage Shipping Zone', i try to manual create new zone type.

After I have create a new zone type, system not allow me to 'add' new zone - the '+' button is grey off.

In the new zone type, i try to 'tick' the button for 'zone creation allowed' - however, system prompt out with the error message 'The message is A record with the value relationship type, forward ref code, backward ref code, subject type, object type already exists. Enter a unique value'

Any idea for this issue?

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