Unable to set Graph Conditional Access Policy Session Controls via PowerShell

Question

I cannot find any documentation on setting the session controls via PowerShell and Microsoft Graph. I've tried experimenting on my own and setting it up similarly to the other conditions, but without any luck.

Here's my code. PowerShell simply says it doesn't match the schema of ConditionalAccessPolicy type, but I'm having trouble finding what it does support, what the full schema includes. It guides me here: https://docs.microsoft.com/en-us/graph/api/conditionalaccessroot-post-policies?view=graph-rest-1.0.

I feel like I'm either missing something, or I've found something that isn't currently supported.