You can check the XML of the prepared invoice, for example, here: https://www.freeformatter.com/xml-validator-xsd.html
XML Input - a file should be uploaded from the computer or the XML content should be copied into this cell
XSD Input (Optional if XSD referred in XML using schemaLocation) - copy or upload the XSD file that defines the rules inside the XML
The XSD file can be found on this website https://www.pangaliit.ee/arveldused/e-arve