Here's an example, the URL that VBSEO uses may look like this:
http://tntu.net/test-forum/4756-ggggg.html

4756 is the thread id.

When I try to use the threadid, or the url, where vbplaza asks: "Thread ID/Thread URL:" on the item page, the item is purchased, but not applied.

Don't know if there's an easy way around that or not.

This would be the "normal" un-vbseo url, that vbseo redirects to the above URL.
http://tntu.net/showthread.php?t=4756

When trying to buy the "close a thread" option, vbplaza tells me that "The thread you are trying to close is in a forum that you are unable to close threads in." which isn't the case.

So vbplaza can find the thread, but it can't update it. Maybe fetch_forum_parent_list or the forumcache doesn't work well with vbseo?