Can't get Lucene to work

The server I use runs Lucee and the provider tells me it has Lucene installed. is a browsable repository of legal texts in HTML form (you need to login though). It would be essential to have a text search function.

On the search page of Lucee web admin, I entered the name of a collection for this and entered the path that contains all those files. “Mapped” is false. What exactly do I have to do to “map” the collection and make these files searchable?

I entered the same path in “directory path” under “Add/Update path index”. Not sure what to enter into the URL field so I entered the same path plus “search.cfm”. And I check “index subdirectories” of course. Correct so far?

When I click “update” now, there is a popup saying “please wait”. Then after a minute or two, I get a 520 “Bad Gateway” error.

The provider tells me they have already increased the webserver timeout. How long should the process take for something like 3,500 html files? (if I have set it up correctly.) For local (CD) versions of this, I run a Javascript search engine, it takes 2-3 minutes to index everything.