I've been using the tutorials here as well as here in order to host a web page using Apache on macOS Catalina Version 10.15.1. The problem was that I couldn't access the localhost and kept getting a 404 error.
Upon entering the line
sudo /usr/sbin/apachectl configtest in the terminal, I get the following error message:
AH00526: Syntax error on line 21 of /private/etc/apache2/extra/httpd-autoindex.conf: Invalid command 'Alias', perhaps misspelled or defined by a module not included in the server configuration.
This was the line that was giving me trouble:
Alias /icons/ "/usr/share/apache2/icons/"