Support for Skybox theme

I’m looking for support for the Skybox WP theme. every time we attempt to start a new post we receive this error message at the top of the post:

“Failed to load plugin url: https://fightforthesoulofthecities.com/wp-content/themes/skybox/functions/thundercodes/thundercodes_plugin.php?dir=https%3A%2F%2Ffightforthesoulofthecities.com%2Fwp-content%2Fthemes%2Fskybox”

I’m not a very technical person, and I was not the one who built the site, (that person is long gone), but now i’m in charge of maintaining the site, and I need your help.