So I created a little video to show you how it works. Actually, you don't have to worry about the link to the survey and how the encID gets there later. Your Panel Provider will create a personalized link for every participant with an individual encID, this here is for testing if it work to pass this encID back to them.
So if what is written after the "&encID=" in the survey link comes out at the end in the end URL, this means things are working.
I created 3 different URLs on an uploaded version of your example LSS and everytime the encID is passed through the survey to the end url, so seems like things are working. I have created a little video to show you how it works:
www.dropbox.com/s/3pwd9r42pyafrqn/limesu...integration.mp4?dl=0
So basically, each respondent will receive such a link and when they click on it, they'll get to your survey, your survey will grab the encID, save it in the hidden question and when the person finishes the end url will contain this encID again, which will redirect them to a page of your panel provider and they will read out this link and update their database accordingly.
you only have to worry, if the encID is passed through correctly and if the different links to the provider are correct.