persistent-workspaces in ext/workspaces not working in mangowc

[Estherenne]

I have this in my config:

"ext/workspaces": {
  "disable-scroll": true,
  "format": "{name}",
  "on-click": "activate",
  "all-outputs": false,
  "persistent-workspaces": {
    "1": [],
    "2": [],
    "3": [],
    "4": [],
    "5": []
  },
},

However, the persistent-workspaces option just doesn't work. No matter what I try, only the active/occupied workspaces are shown.
Posting these here because this is still probably a mistake on my part.
Any help is appreciated.
Thanks in advance.