The starting URL, which provider sends to respondents:
https://www.soscisurvey.de/localness_project1/?r=3-Aj9x9AVH
Great, then you won't need no readGET()
or "Client and transmitted variables" question at all, as r= stores the respondent ID into the REF variable.
In this case use this PHP command to do your redirect (the %reference% placeholder is preset automatically):
redirect('http://www.infovalidator.com/ic/survey.php?autoAnswer[292697][0]=0&encID=%reference%');