I would like to close a topic from PHP.

For this, I tried this:

 WPF()->topic->edit( [ 'topicid' => 1, 'closed' => 1] )

... but this does not close it.

I can't find a solution, but I think this should be called also:

wpforo_clean_cache( 'topic', 1 )

Do I have to call a SQL UPDATE statement directly, or do you have a function for me, doing this?