need help with persistence

[longpanda]

"persistence":[
        {
            "image": "/iso/kali-linux-2021.4a-live-amd64.iso",
            "backend":[
                "/persistence/persistence_ext4_4GB_persistence.dat"
            ],
            "timeout": 10,
            "autosel": 1
        }
    ]

files are placed as above config mentions
but nothing shows up when I boot from kali persistence

 Don't edit ventoy.json manually. Delete it and use VentoyPlugson to generate it.  It will check the json syntax、file existence and filename lower/upper case automatically.
https://www.ventoy.net/en/plugin_plugson.html