Why cant i use checkout form?!

i have a problem. My site works as it should. But i want to edit my checkout page so i was going to use “Checkout Field Editor for WooCommerce” plugin. When i go to the plugin through the eoocommerce meny i get this error message:

Fatal error: Uncaught Error: method_exists(): Argument #1 ($object_or_class) must be of type object|string, null given
in /home/mobilski/mobilskins.se/wp-content/plugins/klarna-checkout-for-woocommerce/classes/class-kco-templates.php on line 203

Call stack:

method_exists()
wp-content/plugins/klarna-checkout-for-woocommerce/classes/class-kco-templates.php:203
KCO_Templates::kco_wc_unrequire_wc_billing_state_field()
wp-includes/class-wp-hook.php:294
WP_Hook::apply_filters()
wp-includes/plugin.php:212
apply_filters()
wp-content/plugins/woocommerce/includes/class-wc-countries.php:1496
WC_Countries::get_address_fields()
wp-content/plugins/woo-checkout-field-editor-pro/includes/utils/class-thwcfd-utils.php:118
THWCFD_Utils::get_fields()
wp-content/plugins/woo-checkout-field-editor-pro/admin/class-thwcfd-admin-settings-general.php:113
THWCFD_Admin_Settings_General::output_content()
wp-content/plugins/woo-checkout-field-editor-pro/admin/class-thwcfd-admin-settings-general.php:66
THWCFD_Admin_Settings_General::render_page()
wp-content/plugins/woo-checkout-field-editor-pro/admin/class-thwcfd-admin-settings-general.php:52
THWCFD_Admin_Settings_General::init()
wp-content/plugins/woo-checkout-field-editor-pro/admin/class-thwcfd-admin.php:138
THWCFD_Admin::output_settings()
wp-includes/class-wp-hook.php:292
WP_Hook::apply_filters()
wp-includes/class-wp-hook.php:316
WP_Hook::do_action()
wp-includes/plugin.php:484
do_action()
wp-admin/admin.php:259

This is under the billing fields.This is under the shipping field:

Fatal error: Uncaught Error: method_exists(): Argument #1 ($object_or_class) must be of type object|string, null given
in /home/mobilski/mobilskins.se/wp-content/plugins/klarna-checkout-for-woocommerce/classes/class-kco-templates.php on line 221

Call stack:

method_exists()
wp-content/plugins/klarna-checkout-for-woocommerce/classes/class-kco-templates.php:221
KCO_Templates::kco_wc_unrequire_wc_shipping_state_field()
wp-includes/class-wp-hook.php:294
WP_Hook::apply_filters()
wp-includes/plugin.php:212
apply_filters()
wp-content/plugins/woocommerce/includes/class-wc-countries.php:1496
WC_Countries::get_address_fields()
wp-content/plugins/woo-checkout-field-editor-pro/includes/utils/class-thwcfd-utils.php:118
THWCFD_Utils::get_fields()
wp-content/plugins/woo-checkout-field-editor-pro/admin/class-thwcfd-admin-settings-general.php:113
THWCFD_Admin_Settings_General::output_content()
wp-content/plugins/woo-checkout-field-editor-pro/admin/class-thwcfd-admin-settings-general.php:66
THWCFD_Admin_Settings_General::render_page()
wp-content/plugins/woo-checkout-field-editor-pro/admin/class-thwcfd-admin-settings-general.php:52
THWCFD_Admin_Settings_General::init()
wp-content/plugins/woo-checkout-field-editor-pro/admin/class-thwcfd-admin.php:138
THWCFD_Admin::output_settings()
wp-includes/class-wp-hook.php:292
WP_Hook::apply_filters()
wp-includes/class-wp-hook.php:316
WP_Hook::do_action()
wp-includes/plugin.php:484
do_action()
wp-admin/admin.php:259

Why do i get this message and how do i solve this?

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