Failed to run the pipeline (Pipeline) - Azure Data Factory

For testing purposes I'm trying to execute this simple pipeline (nothing sophisticated).

However, I'm getting this error:

{"code":"BadRequest","message":null,"target":"pipeline//runid/cb841f14-6fdd-43aa-a9c1-4619dab28cdd","details":null,"error":null}

The goal is to see if two variables are getting the right values (we have been facing some issues in our production environment).

This is the json with the definition of the pipeline:

{
"name": "GeneralTest",
"properties": {
    "activities": [
        {
            "name": "Set variable1",
            "type": "SetVariable",
            "dependsOn": [],
            "userProperties": [],
            "typeProperties": {
                "variableName": "start_time",
                "value": {
                    "value": "@utcnow()",
                    "type": "Expression"
                }
            }
        },
        {
            "name": "Wait1",
            "type": "Wait",
            "dependsOn": [
                {
                    "activity": "Set variable1",
                    "dependencyConditions": [
                        "Succeeded"
                    ]
                }
            ],
            "userProperties": [],
            "typeProperties": {
                "waitTimeInSeconds": 5
            }
        },
        {
            "name": "Set variable2",
            "description": "",
            "type": "SetVariable",
            "dependsOn": [
                {
                    "activity": "Wait1",
                    "dependencyConditions": [
                        "Succeeded"
                    ]
                }
            ],
            "userProperties": [],
            "typeProperties": {
                "variableName": "end_time ",
                "value": {
                    "value": "@utcnow()",
                    "type": "Expression"
                }
            }
        }
    ],
    "variables": {
        "start_time": {
            "type": "String"
        },
        "end_time ": {
            "type": "String"
        }
    },
    "folder": {
        "name": "Old Pipelines"
    },
    "annotations": []
}

}

What am I missing, or what could be the problem with this process?

You are having a "blank space" after the variable name end_time like "end_time "

You can see the difference in my repro: MyCode VS YourCode

Clearing that would make the execution just fine.