JoomMap support Joomla custom fields integration and built-in custom fields, so we do suggest to use Joomla custom fields because we are going to remove old built-in custom fields system in future.
To enable Joomla custom fields, go to Configuration -> Tab locations -> and choose Joomla custom fields in custom fields param -> then save & close
Then go to "Location types" view, then you will see manage fields button on each type, each location type can have it's own custom fields, click on manage fields of location type that you want and start adding fields.
Once done, go to locations , create a new location or edit an existing location, new tab will be displayed that show custom fields inputs. note that custom fields change when changing primary location type.