Removing and reinserting the stripe payment plugin, disabling most other plugins, and enabling only stripe payment, the phenomenon was the same. It seems that coupon.php exists under the stripe payment of wordpress but cannot be read.
Since “Unreadable error” is displayed in Japanese, there may be a problem with the wordpress Japanese environment. How is it? I am in trouble because I cannot use the following. I wonder if can’t open coupon setting view.