I18N Issue

This plugin slug is user-submitted-posts, but your Text Domain is usp. Change this plugin’s Text Domain so it is equal to its slug and modify the text domain in all your source files. This change is needed because your “Requires at least” is below 4.6. (see https://developer.ww.wp.xz.cn/plugins/internationalization/how-to-internationalize-your-plugin/#text-domains)
“Requires at least” (4.1) is below 4.6 so a load_plugin_textdomain is needed. (see https://developer.ww.wp.xz.cn/plugins/internationalization/how-to-internationalize-your-plugin/#loading-text-domain)