API vs. GUI - Delete Writable Volumes Permissions

[mchadwick19]

I'm working to automate cleaning up writable volumes via the API. I have everything built correctly but when I issue this command:

Invoke-RestMethod -WebSession $Login -Method Post -Uri "https://$avServer/cv_api/volumes/delete?bg=0&volumes%5B%5D=$wvToDeleteID"

I get "403 Permission Denied" yet I can delete the same WV using the GUI with the same user account that I accessed the API with.

The account has the pre-built "Writables Administrator" role. I do have a separate account that is a full Admin in AppVolumes and it works in both cases. Just wondering what permission I need to add in order for my scripts to work.