My endpoint was wrong.

here is the correct endpoint url : https://docs.databricks.com/api/azure/account/workspaceassignment/update

this is the correct code

for row in joined_groups_workspace_account.collect():
    group_id = row.id
    group_name = row.displayName

    url = f"https://accounts.azuredatabricks.net/api/2.0/accounts/{databricks_account_id}/workspaces/{workspace_id}/permissionassignments/principals/{group_id}"
    payload = {
    "permissions": ["USER"]
    }

    response = requests.put(url, headers=account_headers, data=json.dumps(payload))

    if response.status_code == 200:
        print(f"✅ Group '{group_name}' added to workspace.")
    elif response.status_code == 409:
        print(f"⚠️ Group '{group_name}' already added to workspace.")
    else:
        print(f"❌ Failed to add group '{group_name}'. Status: {response.status_code}. Response: {response.text}")