Only countries and states that are enabled can be selected in the Manager, for example.
To enable a country
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In the Designer, select the Base data > Localization > Country > Disabled category.
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Select a country.
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Set Enabled.
 
To enable a state
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In the Designer, select the Base data > Localization > Country > <country name> > States category.
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Select a state.
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Set Enabled.