Adding the xsiType=xnat:resource query parameter leads to

error 422: Unprocessable entity

This can be reproduced with curl.
omitting this query parameter solve the issue

Libs/XNAT/Core/ctkXnatResource.cpp

@@ -173,7 +173,6 @@ void ctkXnatResource::downloadImpl(const QString& filename)
 void ctkXnatResource::saveImpl(bool /*overwrite*/)
 {
   ctkXnatSession::UrlParameters urlParams;
-  urlParams["xsiType"] = this->schemaType();
 
   const QMap<QString, QString>& properties = this->properties();
   QMapIterator<QString, QString> itProperties(properties);