Does the site have its own panel to which the questionnaire made on this platform is sent?
No, www.soscisurvey.de provides the software to implement and run the online questionnaire, but we do not offer recruitment of respondents.
Does the VAT have to be with the country prefix or not?
The shop will usually ask for an EU VAT number. That includes a country prefix (and in Swiss even a postfix).
And when I was filling said settings incomplete, and I had already filled everything necessary.
If the form did not specify what was missing, and nothing was marked in red ... that sounds like an error. Apologies for that. Would you mind sending a screenshot of your form to info@soscisurvey.de, please?