Hi, I don't see the link between the variables and the NL-Runtime Error. What error detail do you get?

Regarding the variables, an efficient way is to use compound variables. Let's define the variables:

domain_PROD=myprod.com
domain_TEST=mytestsenv
ENV= PROD or TEST

then use ${domain_${ENV}} as the hostname of your server so you switch all your environment related variables in a single switch.

Note that you can change the ENV constant variable through the command line for your automated tests. (see launching a tests from the command line in the documentation)