question

Can you give us the Title ID in question, and the PlayFab ID of a player account you're using for this test?

I had the same issue,

The data you receive from "GetUserReadOnlyDataResponse.Data["CheckInTracker"].Value" seems not to be a valid string but something like an "object".

The way i resolved it is to call JSON.Stringify to cast your json in a valid string. Then you can parse it again with JSON.Parse.

Try to modify your line 14 : tracker = JSON.parse(JSON.stringify(GetUserReadOnlyDataResponse.Data["CheckInTracker"].Value));

I finally found the problem thank to @paulcmoi51 who hint me about "string" part.

Here a little more of debugging and it say every thing.

		var dataValue = GetUserReadOnlyDataResponse.Data["CheckInTracker"].Value;

		log.info("dataValue");
		log.info(dataValue);

		log.info("JSON.parse dataValue");
		tracker = JSON.parse(dataValue, (_key, _val) => {
			log.info("[] " + _key + " | " + _val + " ]");
			return _val;
		});

		log.info("tracker");
		log.info(tracker);
//The log would be
// dataValue
// "{\"LoginStreak\":1,\"NextEligibleGrant\":1490183204031}" // clearly a string
// JSON.parse dataValue
// [  | {"LoginStreak":1,"NextEligibleGrant":1490183204031} ] // the key is empty with this object as value.
// tracker
// {"LoginStreak":1,"NextEligibleGrant":1490183204031} // look normal but can't access via tracker variable.	

So the root of all problem was my JSON in Player Data(Title) should not be like this.

"{\"LoginStreak\":1,\"NextEligibleGrant\":1490183204031}"

But Like this instead.

{"LoginStreak":1,"NextEligibleGrant":1490183204031}

So I Change the code where I save my data like this

function UpdateTrackerData(data) {
	var UpdateUserReadOnlyDataRequest = {
		"PlayFabId": currentPlayerId,
		"Data": {}
	};
	//FROM
	UpdateUserReadOnlyDataRequest.Data[CHECK_IN_TRACKER] = JSON.stringify(data);
	//TO
	UpdateUserReadOnlyDataRequest.Data[CHECK_IN_TRACKER] = data;

	server.UpdateUserReadOnlyData(UpdateUserReadOnlyDataRequest);
}

The function "UpdateTrackerData" was a function I copy from PlayFab ProgressiveRewardsRecipe. Please fix it.

Ps. Apology for my bad grammar. English is not my native langauge.

know this is an old topic but no answer here really fixes the problem in the recipe's CloudScript, the problem is that when you first enter the script leads you to the ResetTracker function which returns a stringified value from reset which is assigned to tracker, so when the tracker is sent to UpdateTrackerData(data) it is sent as a string instead of a JSON variable which is what the UpdateTrackerData function expects, so the result of using stringify on a string is the string having these '\' before the quotes which is sent to the CheckInTracker on Player data and when you JSON.parse it you still have a string so if you try using tracker[TRACKER_NEXT_GRANT] you will get a null value.

The solution is simple in the return statement from the ResetTracker function switch this

return JSON.stringify(reset);

with this

return JSON.parse(JSON.stringify(reset));

I hope I helped anyone still having this problem and hope the recipe's CloudScript gets fixed soon