Problem with the domain questionnaire

Sorry for the trouble but i cant’t find a solution for this problem at the FAQ.
I created a survey in CAWI mode, I was able to configure everything without problems (including sending the questionnaires) but when the recipient wants to do the questionnarie, a domain not found screen pops up (which I leave attached). If I correct the domain, you can enter the questionnaire perfectly.

So, what o how can i do to fix this?
Sorry if my english is not the best, its not my first language.