Help: how to modify items in array

[gzliudan]

When I replace a string KV with json object in a array, json report an error:
[json.exception.type_error.302] type must be string, but is object

My codes likes below:

json_t obj = json_t::parse(str1);
json_t& items = obj["items"];      
for (auto& item : items) {
    std::string str2 = handle_data(item["data"].get<std::string>()); 
    action["data"] = json_t::parse(str2);
}

orgin json string is like below:

{
    "items": [
        {
            "id": "123",
            "data":"1f75620e7e"
        },
        {
            "id": "456",
            "data":"afd3e1d8b3"
        }
    ]
}

I want to replace each item's data field with a new json object, the result will likes below:

{
    "items": [
        {
            "id": "123",
            "data":{"k1":"v1", "k2":"v2"}
        },
        {
            "id": "456",
            "data":{"k1":"v3", "k2":"v4"}
        },
    ]
}

[gzliudan]

The problem is resolved, it's my log code raised exception after change type from string to object:

LogInfo("new data={}", action.at("data").get<std::string>());