Accessing class file in App_Code

While working on my FTP server, I am trying to access a class within my App_Code, but it is not working.
When writing, the class is accessible/usable in the code like shown in picture. I get no build errors.





But when I run it in the browser, I get an error stating that it cannot find my class.




I've looked around some other posts on the forum, like using namespace, but it didn't work. Would anyone know how to fix this?

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