RP4VM Rest API - Create Bookmark

Hello - I'm trying to navigate some REST commands on RP4VM 5.2 so I can avoid using the awful Flash interface, but the REST documentation is very vague and limited. What I want to do is be able to take bookmark snapshots at a specific time of day for a group set. I have found the location, but the json body that has to be included is where I'm confused. I'm using powershell and the invoke-restmethod command, like below:

Invoke-RestMethod -Method POST -Uri https://{CLUSTER_IP}:443/fapi/rest/5_2/group_sets/subsets/snapshots -Credential admin -Body ????

After reviewing the object browser, it appears it needs a json body element, but I can't seem to find what parameters need to be passed. I'm assuming it's something like: groupSetId, bookmarkName, consolidationPolicy, consistencyType, however none of those combos seem to work. Is there any further documentation, or something that can point me in the right direction? 

Thanks!