How to modify Json Payload

I’m trying to do something like this:

IF INTKEY @SR_LENGTH EqualTo 9

LOG payload["solution"]["interrogation"]["sr"] = SR + "0";

END

Log is returning "Not possible to convert String to Int. Any Clue?
I need to change one value from the Json payload. I know this can be done by grabbing all json values and then building the payload back, but I was wondering if there was any way to access this payload directly and edit it in the lolicode.

You can use Newtonsoft.Json to deserialize, change a value, then serialize again, but you do need C# knowledge in order to do this.