The kirki_config argument is used internally to assign a configuration to your fields.

You don’t have to manually set it since it’s automatically set when you create your field.

Example:

Kirki::add_field( 'my_config', [
    'type'        => 'text',
    'settings'    => 'my_setting',
    'label'       => esc_html__( 'Text Control', 'kirki' ),
    'section'     => 'my_section',
    'default'     => esc_html__( 'This is a default value', 'kirki' ),
    'priority'    => 10,
] );

In the above example, the kirki_config argument is automatically set to my_config.