Hello,
If you need to solve the issue faster, you can write us an email (support@kentico.com) next time, if you have valid maintenance. Anyway, I was able to reproduce this issue. Regrettably, the fact that the {%GetDocumentUrl() %} method is not resolved in the Text/XML transformation seems to be a bug in the current version of Kentico CMS. We will try to fix it in the next hotfix for the current version of Kentico
CMS. Thank you for letting us know about this issue.
Best regards,
Michal Legen