The parameters return from the GET.../parameters is empty:
<?xml version="1.0" encoding="UTF-8" standalone="yes" ?>
<parameters />
What I do is call a POST/PUT.../datafilter with the <datafilter><and><condition key="[dataprovider]" operator="Equal"><value>my value</value></condition></and></datafilter> which fails with an error:
<error><error_code>WSR 00400</error_code> <message>The expression "[dataprovider]" can't be found in the document dictionary. Please enter another expression.</message></error>