If the server is already running, press Ctrl+C, set the variable, then start it again. Keep the key on the server: do not paste it into index.html or share it with classmates. Without the key, the ...
See also: server-side-advanced.md for Part 1 (ExifTool, Go rune/byte mismatch, zip symlink traversal, path traversal bypasses, Flask/Werkzeug debug, XXE external DTD, WeasyPrint SSRF, MongoDB regex ...