How to set both key and value pair as variable

[hf81-ble]

Describe the bug
I want to write a generic storage handler into an json file. Key and value are variables

void setSetting ( CString key, Integer value)
{
Json::Value data;
data[key] = value;
///write json
}

Result in VS2022 Compiler:
Severity Code Description Project File Line Suppression State
Error C2678 binary '[': no operator found which takes a left-hand operand of type 'Json::Value' (or there is no acceptable conversion) Editor ConfigJson.cpp 61

To Reproduce
Steps to reproduce the behavior:

1. Use a variable as key instead of a static String

Expected behavior
should write the key/pair pair

Desktop (please complete the following information):

• OS: Win10
• Visual Studio 2022