In the end, the name of the panel provider's ID variable in Lighthouse Studio does not matter. You could name it "abcde" if you wanted. You would be able to pass the variable back to your panel provider through their re-direct link as long as your panel provider inserted the actual ID correctly into the one-click link.
You are receiving an error message because of the "_" in "Strans_id". Lighthouse Studio does not allow this special character for variable names. You could name it Stransid to make it clear to your panel provider that they need to replace VALUE in Stransid=VALUE with the actual value.
Feel free to call or email our support team (firstname.lastname@example.org or +1 801 477 4700) if you have additional questions.