Initially OK Tech was not meant to be called from Moodle 2.0 infrastructure and had (and still have) its own authentication process and wsdl emission.
If you want to 'see' the oktech operations under Moodle 2.0 admins screens you must copy the content of folder wspp/moodle2integration (i.e the folder named oktech) in Moodle's local directory AND visit the Notifications link of site administration. See the README file within that folder
Currently your 'call' works (and returns quite a well formed WSDL) if you comment out line 885 of webservice/lib.php that states :
throw new moodle_exception('erroroptionalparamarray', 'webservice', '', $name);
This is due to the fact that the structures named 'datum' declared in local/oktech/oktech_classlib.php and used in all add_xxx and update_xxxx operations are erroneously declared as optional by the lines :
where they should be
I shall try to fix this real soon...
EDIT : this has been just fixed of github see latest commit , so not need to change Moodle 2.0 official code
(pick up the latest oktech_classlib.php file and copy it in your local/oktech folder...
Furthermore OK Tech has its own 'standard wsdl' that can be reached at