AWS Step functions Api Gateway integration RequestBody.$ bug

Question

I have a state machine splitted in some different lambdas to complete a process. One of the steps is a call to apigateway lambda function. Previous call is a call to lambda function and in ASL language I tell to pass the object overrided by this function to the next step.  
  
When it comes to Apigateway step, PathParameters are filled ok with the jsonpath accessors but when I try to use in RequestBody the received value are always empty.  
  
I'm using golang language  
  
State Machine  
"UploadFile": {  
            "Type": "Task",  
            "Resource": "${UploadFileFunctionArn}",  
            "Retry": \[  
                {  
                    "ErrorEquals": \[  
                        "States.TaskFailed"  
                    ],  
                    "IntervalSeconds": 2,  
                    "MaxAttempts": 3,  
                    "BackoffRate": 2.0  
                }  
            ],  
            "Catch": \[  
                {  
                    "ErrorEquals": \[  
                        "States.ALL"  
                    ],  
                    "ResultPath": null,  
                    "Next": "Fail"  
                }  
            ],  
            "ResultPath": "$",  
            "Next": "UpdateTerminal"  
        },  
        "UpdateTerminal": {  
            "Type": "Task",  
            "Next": "HasBeenUpdated",  
            "Resource": "${UpdateTerminalFunctionArn}",  
            "Parameters": {  
                "ApiEndpoint": "${APIDomainName}/${APIBasePath}",  
                "Method": "POST",  
                "Stage": "${ApiStageName}",  
                "Path": "",  
                "PathParameters": {  
                    "terminalId.$": "$.terminalId"  
                },  
                "RequestBody.$": "$",  
                "AuthType": "NO_AUTH"  
            },  
            "Retry": \[  
                {  
                    "ErrorEquals": \[  
                        "States.TaskFailed"  
                    ],  
                    "IntervalSeconds": 2,  
                    "MaxAttempts": 3,  
                    "BackoffRate": 2.0  
                }  
            ]  
        },  
  
Update terminal lambda logs :  
  
fmt.Println("request.Body", request.Body)  
	fmt.Println("request.PathParameters\['terminalId']", request.PathParameters\["terminalId"])  
  
	2020-12-07T13:55:23.889+01:00	request.Body  
	2020-12-07T13:55:23.889+01:00	request.PathParameters\['terminalId'] dc725a3a-0b96-4b14-8036-5c36514466556  
  
Edited by: eguzkilorebeltza on Dec 7, 2020 5:08 AM

Answer

I could solve this isuse after so many different tries. In golang I found that you have to specify in Parameters object **Body** field not as documentation says RequestBody   
  
"Body.$": "States.JsonToString($)",

"UpdateTerminal": {  
            "Type": "Task",  
            "Next": "HasBeenUpdated",  
            "Resource": "${UpdateTerminalApiFunctionArn}",  
            "Parameters": {  
                "ApiEndpoint": "${APIDomainName}/${APIBasePath}",  
                "Method": "POST",  
                "Stage": "${ApiStageName}",  
                "Path": "",  
                "PathParameters": {  
                    "terminalId.$": "$.terminalId"  
                },  
                **"Body.$": "States.JsonToString($)",**  
                "AuthType": "NO_AUTH"  
            },  
            "Retry": \[  
                {  
                    "ErrorEquals": \[  
                        "States.TaskFailed"  
                    ],  
                    "IntervalSeconds": 2,  
                    "MaxAttempts": 3,  
                    "BackoffRate": 2.0  
                }  
            ]  
        },

AWS Step functions Api Gateway integration RequestBody.$ bug

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