error proceeding checkout

when use sofort option payment at check out error proceeding checkout show
the error says WC_Countries::get_base_country() should not be called statically
the error log

[23-Apr-2019 09:05:19 UTC] order_key was called incorrectly. Order properties should not be accessed directly. Backtrace: require('wp-blog-header.php'), require_once('wp-includes/template-loader.php'), do_action('template_redirect'), WP_Hook->do_action, WP_Hook->apply_filters, WC_AJAX::do_wc_ajax, do_action('wc_ajax_checkout'), WP_Hook->do_action, WP_Hook->apply_filters, WC_AJAX::checkout, WC_Checkout->process_checkout, WC_Checkout->process_order_payment, WC_Gateway_Sofort->process_payment, WC_Abstract_Legacy_Order->__get, wc_doing_it_wrong. This message was added in version 3.0.
[23-Apr-2019 09:05:19 UTC] PHP Notice:  Undefined offset: 1 in /home/otyxfvhr/maison-zoe.com/wp-content/plugins/woo-sofortuberweisung-gateway/sofort/core/sofortLibAbstract.inc.php on line 533
[23-Apr-2019 09:05:19 UTC] PHP Notice:  Undefined offset: 2 in /home/otyxfvhr/maison-zoe.com/wp-content/plugins/woo-sofortuberweisung-gateway/sofort/core/sofortLibAbstract.inc.php on line 533
[23-Apr-2019 09:05:19 UTC] PHP Notice:  Undefined offset: 1 in /home/otyxfvhr/maison-zoe.com/wp-content/plugins/woo-sofortuberweisung-gateway/sofort/core/abstractDataHandler.php on line 210
[23-Apr-2019 09:05:19 UTC] PHP Notice:  Undefined offset: 2 in /home/otyxfvhr/maison-zoe.com/wp-content/plugins/woo-sofortuberweisung-gateway/sofort/core/abstractDataHandler.php on line 210
[23-Apr-2019 09:05:19 UTC] PHP Notice:  Undefined offset: 1 in /home/otyxfvhr/maison-zoe.com/wp-content/plugins/woo-sofortuberweisung-gateway/sofort/core/sofortLibHttp.inc.php on line 234
[23-Apr-2019 09:05:19 UTC] PHP Notice:  Undefined offset: 2 in /home/otyxfvhr/maison-zoe.com/wp-content/plugins/woo-sofortuberweisung-gateway/sofort/core/sofortLibHttp.inc.php on line 234
[23-Apr-2019 09:05:19 UTC] PHP Deprecated:  Non-static method WC_Countries::get_base_country() should not be called statically in /home/otyxfvhr/maison-zoe.com/wp-content/plugins/woo-sofortuberweisung-gateway/woo-sofortuberweisung-gateway.php on line 254
[23-Apr-2019 09:06:49 UTC] The WC_Product::get_price_excluding_tax function is deprecated since version 3.0. Replace with wc_get_price_excluding_tax.
[23-Apr-2019 09:07:11 UTC] order_key was called incorrectly. Order properties should not be accessed directly. Backtrace: require('wp-blog-header.php'), require_once('wp-includes/template-loader.php'), do_action('template_redirect'), WP_Hook->do_action, WP_Hook->apply_filters, WC_AJAX::do_wc_ajax, do_action('wc_ajax_checkout'), WP_Hook->do_action, WP_Hook->apply_filters, WC_AJAX::checkout, WC_Checkout->process_checkout, WC_Checkout->process_order_payment, WC_Gateway_Sofort->process_payment, WC_Abstract_Legacy_Order->__get, wc_doing_it_wrong. This message was added in version 3.0.
[23-Apr-2019 09:07:11 UTC] PHP Notice:  Undefined offset: 1 in /home/otyxfvhr/maison-zoe.com/wp-content/plugins/woo-sofortuberweisung-gateway/sofort/core/sofortLibAbstract.inc.php on line 533
[23-Apr-2019 09:07:11 UTC] PHP Notice:  Undefined offset: 2 in /home/otyxfvhr/maison-zoe.com/wp-content/plugins/woo-sofortuberweisung-gateway/sofort/core/sofortLibAbstract.inc.php on line 533
[23-Apr-2019 09:07:11 UTC] PHP Notice:  Undefined offset: 1 in /home/otyxfvhr/maison-zoe.com/wp-content/plugins/woo-sofortuberweisung-gateway/sofort/core/abstractDataHandler.php on line 210
[23-Apr-2019 09:07:11 UTC] PHP Notice:  Undefined offset: 2 in /home/otyxfvhr/maison-zoe.com/wp-content/plugins/woo-sofortuberweisung-gateway/sofort/core/abstractDataHandler.php on line 210
[23-Apr-2019 09:07:11 UTC] PHP Notice:  Undefined offset: 1 in /home/otyxfvhr/maison-zoe.com/wp-content/plugins/woo-sofortuberweisung-gateway/sofort/core/sofortLibHttp.inc.php on line 234
[23-Apr-2019 09:07:11 UTC] PHP Notice:  Undefined offset: 2 in /home/otyxfvhr/maison-zoe.com/wp-content/plugins/woo-sofortuberweisung-gateway/sofort/core/sofortLibHttp.inc.php on line 234
[23-Apr-2019 09:07:11 UTC] PHP Deprecated:  Non-static method WC_Countries::get_base_country() should not be called statically in /home/otyxfvhr/maison-zoe.com/wp-content/plugins/woo-sofortuberweisung-gateway/woo-sofortuberweisung-gateway.php on line 254
[23-Apr-2019 09:20:33 UTC] order_key was called incorrectly. Order properties should not be accessed directly. Backtrace: require('wp-blog-header.php'), require_once('wp-includes/template-loader.php'), do_action('template_redirect'), WP_Hook->do_action, WP_Hook->apply_filters, WC_AJAX::do_wc_ajax, do_action('wc_ajax_checkout'), WP_Hook->do_action, WP_Hook->apply_filters, WC_AJAX::checkout, WC_Checkout->process_checkout, WC_Checkout->process_order_payment, WC_Gateway_Sofort->process_payment, WC_Abstract_Legacy_Order->__get, wc_doing_it_wrong. This message was added in version 3.0.
[23-Apr-2019 09:20:33 UTC] PHP Notice:  Undefined offset: 1 in /home/otyxfvhr/maison-zoe.com/wp-content/plugins/woo-sofortuberweisung-gateway/sofort/core/sofortLibAbstract.inc.php on line 533
[23-Apr-2019 09:20:33 UTC] PHP Notice:  Undefined offset: 2 in /home/otyxfvhr/maison-zoe.com/wp-content/plugins/woo-sofortuberweisung-gateway/sofort/core/sofortLibAbstract.inc.php on line 533
[23-Apr-2019 09:20:33 UTC] PHP Notice:  Undefined offset: 1 in /home/otyxfvhr/maison-zoe.com/wp-content/plugins/woo-sofortuberweisung-gateway/sofort/core/abstractDataHandler.php on line 210
[23-Apr-2019 09:20:33 UTC] PHP Notice:  Undefined offset: 2 in /home/otyxfvhr/maison-zoe.com/wp-content/plugins/woo-sofortuberweisung-gateway/sofort/core/abstractDataHandler.php on line 210
[23-Apr-2019 09:20:33 UTC] PHP Notice:  Undefined offset: 1 in /home/otyxfvhr/maison-zoe.com/wp-content/plugins/woo-sofortuberweisung-gateway/sofort/core/sofortLibHttp.inc.php on line 234
[23-Apr-2019 09:20:33 UTC] PHP Notice:  Undefined offset: 2 in /home/otyxfvhr/maison-zoe.com/wp-content/plugins/woo-sofortuberweisung-gateway/sofort/core/sofortLibHttp.inc.php on line 234
[23-Apr-2019 09:20:33 UTC] PHP Deprecated:  Non-static method WC_Countries::get_base_country() should not be called statically in /home/otyxfvhr/maison-zoe.com/wp-content/plugins/woo-sofortuberweisung-gateway/woo-sofortuberweisung-gateway.php on line 254
[23-Apr-2019 09:21:45 UTC] order_key was called incorrectly. Order properties should not be accessed directly. Backtrace: require('wp-blog-header.php'), require_once('wp-includes/template-loader.php'), do_action('template_redirect'), WP_Hook->do_action, WP_Hook->apply_filters, WC_AJAX::do_wc_ajax, do_action('wc_ajax_checkout'), WP_Hook->do_action, WP_Hook->apply_filters, WC_AJAX::checkout, WC_Checkout->process_checkout, WC_Checkout->process_order_payment, WC_Gateway_Sofort->process_payment, WC_Abstract_Legacy_Order->__get, wc_doing_it_wrong. This message was added in version 3.0.
[23-Apr-2019 09:21:45 UTC] PHP Notice:  Undefined offset: 1 in /home/otyxfvhr/maison-zoe.com/wp-content/plugins/woo-sofortuberweisung-gateway/sofort/core/sofortLibAbstract.inc.php on line 533
[23-Apr-2019 09:21:45 UTC] PHP Notice:  Undefined offset: 2 in /home/otyxfvhr/maison-zoe.com/wp-content/plugins/woo-sofortuberweisung-gateway/sofort/core/sofortLibAbstract.inc.php on line 533
[23-Apr-2019 09:21:45 UTC] PHP Notice:  Undefined offset: 1 in /home/otyxfvhr/maison-zoe.com/wp-content/plugins/woo-sofortuberweisung-gateway/sofort/core/abstractDataHandler.php on line 210
[23-Apr-2019 09:21:45 UTC] PHP Notice:  Undefined offset: 2 in /home/otyxfvhr/maison-zoe.com/wp-content/plugins/woo-sofortuberweisung-gateway/sofort/core/abstractDataHandler.php on line 210
[23-Apr-2019 09:21:45 UTC] PHP Notice:  Undefined offset: 1 in /home/otyxfvhr/maison-zoe.com/wp-content/plugins/woo-sofortuberweisung-gateway/sofort/core/sofortLibHttp.inc.php on line 234
[23-Apr-2019 09:21:45 UTC] PHP Notice:  Undefined offset: 2 in /home/otyxfvhr/maison-zoe.com/wp-content/plugins/woo-sofortuberweisung-gateway/sofort/core/sofortLibHttp.inc.php on line 234
[23-Apr-2019 09:21:45 UTC] PHP Deprecated:  Non-static method WC_Countries::get_base_country() should not be called statically in /home/otyxfvhr/maison-zoe.com/wp-content/plugins/woo-sofortuberweisung-gateway/woo-sofortuberweisung-gateway.php on line 254

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