If you search the forum for luup intercept you will find a significant number of posts. Some of these date back to the very early days, but are still relevant. This is one such
In my implementation of openLuup, a Vera emulation environment, I have always struggled with this, and never achieved consensus within the community on how it does/should work.
Suffice to say that this is an appallingly badly ‘designed’ and implemented functionality. I would follow the sage advice of @futzle from the above thread
She was a true expert on such matters, and sadly rarely participates in the forum these days… a huge loss.
Abandon Vera’s flawed approach, use the LuaSocket library for low-level I/O, and roll your own state machine, per her advice.