Courseware tends to produce highest overall revenue in following forms...

1) Initial sale.

2) Monthly/Yearly subscriptions to forums or support.

3) High dollar coaching.

4) High dollar consulting.

Coaching tends to take the form of conversations geared toward assisting a client creating some outcome.

Consulting tends to take the form of hourly work done.

For example, one of my businesses is private, high speed, WordPress hosting.

Coaching, might take the form of assisting a client work out how they might design a system or hire people to develop a large codebase.

Consulting, might take the form of migrating their site to faster hosting... or auditing their code + fixing performance problems... or writing a large codebase.

Truly passive income resembles interest on securities.

Tech related passive income is more quasi-passive, than pure-passive.

For example, say you write an IOS App, every time Apple changes their APIs, your App has the potential of either failing to work or getting booted from the App store, until you or someone updates the code to make the App compliant with new APIs.

If you write a book, you best be making updates to your book repeatedly to keep your book current.

If you run a membership site, then you're taking some serious work to keep people engaged + provide continual + new value.

Domain speculation == Roulette.

I've sold domains for 5 figures + never on purpose.

Best to stick with something you love doing every day, with or without pay, then ask people's assistance about how to monetize what you already do.