Error:

Contents of "/opt/lampp/var/proftpd/start.err":
2023-11-10 10:20:35,788 ip-172-31-5-87 proftpd[191998]: fatal: unknown configuration directive 'function' on line 44 of '/opt/lampp/etc/proftpd.conf'

Solution:

There appears to be an unknown configuration directive ‘function’ on line 44 of the ProFTPD configuration file (/opt/lampp/etc/proftpd.conf), according to the error message. To remedy this, take these actions:

Step 1: Open the ProFTPD configuration file in a text editor. For example, you can use nano:

sudo nano /opt/lampp/etc/proftpd.conf

Step 2: Navigate to line 44 and check for the ‘function’ directive. If it’s not a valid ProFTPD directive, you need to correct it or comment it out. For example, if it looks like this:

Comment it out by adding a # at the beginning of the line:

Step 3: Save the changes and exit the text editor (in nano, you can do this by pressing Ctrl + O to write changes, then Enter to confirm, and Ctrl + X to exit).

Step 4: Restart ProFTPD to apply the changes:

sudo /opt/lampp/lampp restart

Then try to start your server again, it should work now.