Thanks a lot for the lightning-fast response! I get no syntax errors in the validation tool. Also, the survey works fine in the preview mode. However, I’m still unable to fix the error message in the Kobocollect app.
The second part I observed when scanning your XLSForm is that it uses - as shown in the image shared below:
Could you also replace the - with _ (underscore) please?
Would you first fix these and test them again to see if these fix should solve your issue? Feel free to share your XLSForm if the issue is still on. Maybe the community should then also be able to debug your issue further.