Everything worked well. Many thanks for the tip.

I have now saved the files to be edited in:

D:\IRIS\src\...
 

But is it normal that I have to have a separate folder in the "src\csp\"? Because if I simply edit the .csp in the "csp" folder and compile it, I get the "Non-JSON response" error again.
This in itself is not a problem for me, I just want to understand what triggers this error.

I just checked the Management Portal and had to change the path of the web application.

The path was at:
C:\InterSystems\IRIS\CSP\goerke\

Then I changed the path to
C:\InterSystems\IRIS\CSP\goerke\src\csp\goerke

And that solved the problem and everything works as it should and I can start programming.

Thank you for your help!

I think the 2 pictures explain this quite well:

Before compiling:
 

After compiling:
 

In the second image, the index.csp has been added at the bottom after compilation. It is also present in the directory:
 

I'm not following any particular path. I wanted to work on it outside of my internship and create and test a few little things myself to get a feel for it.

The compiling and so on is working so far, but is it normal that it recreates the file in the root directory of the namespace?

Thank you very much, that has helped me. But now I get another error message that I can't do anything with:

"Non-JSON response to /iris/api/atelier/v8/GOERKE/doc/csp%5Cindex.csp?ignoreConflict=1 request. Is the web server suppressing detailed errors?"