Help/Support post data tampering

[keithcis 0 iPhone 6 Plus]

Hello guys,

I was playing on Charles Proxy and watching on the requests made by the game to their server..

I tried tampering their data (man in the middle) eg: changing HP values.. but it seems they know that the data is already tampered and returns an error.

Question:

How did they know that the data is tampered in the first place?

Any ideas will be helpful.

 

*** english is not my first language, please patient with me  TY***

 

{
    "FunctionName": "arbitrateAttacker",
    "FunctionParameter": {
        "ReqVersion": 3,
        "ReqSeq": 324,
        "ClientVersion": "1.18.5",
        "Params": "{\"FightOrigin\":2,\"FighterId\":\"99c9e07c-4ae7-457a-aeed-1d174d0c94ce\",\"HP\":1}",
        "ReqTime": 1537119045,
        "Sign": "64adbacf3be28a8f69d1c1d62e26e42f"
    },
    "RevisionSelection": "Specific",
    "SpecificRevision": 117,
    "GeneratePlayStreamEvent": true
}
//response
{
	"code": 200,
	"status": "OK",
	"data": {
		"FunctionName": "arbitrateAttacker",
		"Revision": 117,
		"FunctionResult": {
			"response": {},
			"auxiliar": null,
			"error_code": 400,
			"error_message": "Bad request",
			"cloudscript_revision": 117
		},
		"Logs": [],
		"ExecutionTimeSeconds": 0.014,
		"ProcessorTimeSeconds": 0,
		"MemoryConsumedBytes": 0,
		"APIRequestsIssued": 0,
		"HttpRequestsIssued": 0
	}
}