What is the exact error message? Maybe share some code?
Have you referenced the right libraries?
I don't know Pascal much, I spent probably less than 50 hours programming in Pascal in my whole life, so I can't remember much. Is it possible that the graph module may not come with Pascal out of the box and might not be installed on the Online GDB server?
Actually, thinking about it, probably it is not installed. The reason is that you can see only character output (standard output). So there's no reason to install a module that supports 2D and 3D drawing when the server will never relay the created scene to the client.