Protect a certain URL/folder in Wordpress site

I have a website build on Wordpress and Formidable Pro plugin, that sends some json data to an external site for each form submission. I have created a directory, where I can view the sent json data for each form submission, that can be accessed with a url that ends with a unique key for each dataset. I need to increase the security there, so it´s only users with administrator access on my site that can access this. I can not give away login details, so I need to be instructed by the freelancer to how to accomplish this. I have researched if there is any restrict access plugins that can do this, but I have not managed to find a plugin that lets me restrict access to a specific url that starts with [login to view URL]