String escaping is the feature that allows to have special characters in your encoded string.

For example:

DynamicJsonBuffer jsonBuffer;
JsonObject& root = jsonBuffer.createObject();
root["hello"] = "[1,2,3]";
root.printTo(Serial);

would print:

{"hello":"[1,2,3]"}

If you want to disable string escaping, you need to wrap the char* with a RawJson, like this:

DynamicJsonBuffer jsonBuffer;
JsonObject& root = jsonBuffer.createObject();
root["hello"] = RawJson("[1,2,3]");
root.printTo(Serial);

which would print:

{"hello":[1,2,3]}