get_used_coupons deprecated

I am getting this error in my logs:

[25-Jun-2020 19:45:15 UTC] PHP Deprecated:  get_used_coupons is <strong>deprecated</strong> since version 3.7! Use WC_Abstract_Order::get_coupon_codes instead. in /home/username/public_html/wp/wp-includes/functions.php on line 4713
[25-Jun-2020 19:45:16 UTC] PHP Notice:  payment_method was called <strong>incorrectly</strong>. Order properties should not be accessed directly. Backtrace: require('wp-blog-header.php'), require_once('wp-includes/template-loader.php'), include('/themes/storefront/page.php'), get_template_part, locate_template, load_template, require('/themes/storefront/content-page.php'), do_action('storefront_page'), WP_Hook->do_action, WP_Hook->apply_filters, storefront_page_content, the_content, apply_filters('the_content'), WP_Hook->apply_filters, do_shortcode, preg_replace_callback, do_shortcode_tag, WC_Shortcodes::checkout, WC_Shortcodes::shortcode_wrapper, WC_Shortcode_Checkout::output, WC_Shortcode_Checkout::order_pay, wc_get_template, include('/plugins/woocommerce-gateway-sagepay-form/assets/templates/order-receipt.php'), do_action('woocommerce_receipt_sagepaydirect'), WP_Hook->do_action, WP_Hook->apply_filters, WC_Gateway_Sagepay_Direct->authorise_3dsecure, Sagepay_Direct_3DSecure_4->authorise, WC_Gateway_Sagepay_Direct->process_response, Sagepay_Direct_ in /home/username/public_html/wp/wp-includes/functions.php on line 5167

I believe it is coming from this plugin, can you help me?