No worries on the basic questions!

Yes- we did install and it does protect content such as articles.

Took Item ID OUT - no luck - still displays everything in Kunena.

Not sure I quite understand what you are asking, but here goes.

In the subscription I setup - call it Plan "A"

I have told it that if you buy Plan A you can ONLY access a single forum topic.

So its: Kunena forum - topic, topic, topic and posts in each. Plan a equates to allowing access to TOPIC "A" only.

I obtained that URL by visiting the forum - noting the URL, and pasting it in the PROTECT URL Field.

I got there from: PLAN (from plugin) - then select the PLAN A - then I selected Integrations, Then Extensions.

From there I tried both protecting Kunena and Not protecting Kunena,

but in the box: BY URL PARTS I have this:

option=com_kunena&func=listcat&catid=6

Only. That is the way I understand from all the posts here, and the docs. However now when I subscribe to PLAN A I see Kunena and ALL forums, topics, posts

not the Posts for the TOPIC in Plan A.

Hopefully that is what you're asking - thanks for the help!

"For that you would need a specific Kunena integrations plugin (that doesn't exist yet), and probably changes in Kunena too..."

Is there any such Subs plugin for any forum or forum component, currently?

Is there any estimated timeline?

Thanks,
Ken