Passing Arrays to SDM Web Service Operator

Hello,

There are multiple methods in the SDM web interface which require that a list of attributes be passed as a parameter.

For example, the getListValues method, which has the 'attributeNames' parameter.

I feel a bit dense, but I seem to be unable to figure out how to pass multiple attributes -

Passing a single attribute, such as 'ref_num' works just fine, but I can't figure out the syntax for multiple attributes here -

Specifying an array like "['ref_num','open_date ']" results in an error, whereas a comma delimited list like 'ref_num','open_date' returns only the first value.

Here's a screenshot for more detail:

I feel like I'm missing something rather basic here - Does anyone have any advice on what the appropriate syntax here is?