Why whatsapp embedded signup for Tech Provider crushed with "This account wasn't shared" error?

Question

Hello and thank you for your time

I want create integration with whatsapp cloud api as Tech Provider - https://developers.facebook.com/docs/whatsapp/cloud-api/get-started-for-tech-providers/, so i setup everything to be right, but i have some strange error with summary i can't understand or google:

{
    "data": {
        "xfb_update_whatsapp_business_account": null
    },
    "errors": [
        {
            "message": "A server error field_exception occured. Check server logs for details.",
            "severity": "CRITICAL",
            "mids": [
                "c0f5eaac3e14fedde341e0585a08aa80"
            ],
            "code": 2494029,
            "api_error_code": 100,
            "summary": "This account wasn't shared",
            "description": "Something went wrong. Please contact support for more info.",
            "description_raw": "Something went wrong. Please contact support for more info.",
            "is_silent": false,
            "is_transient": false,
            "is_not_critical": false,
            "requires_reauth": false,
            "allow_user_retry": false,
            "debug_info": null,
            "query_path": null,
            "fbtrace_id": "GSFg3mrbfJe",
            "www_request_id": "A3sU1R0gNcSOZ0A3O1YIiRw",
            "path": [
                "xfb_update_whatsapp_business_account"
            ]
        }
    ],
    "extensions": {
        "is_final": true
    }
}

Is there any guidance, what should i do to pass this error and continue whatsapp embedded signup flow?