Hi All,
 
Getting this error message while validating challenge #3 of superbadges.

There was an unhandled exception. Please reference ID: VTREZLDW. Error: Restforce::ResponseError. Message: 550: Cannot convert dynamic parameters of a reference line in chart widgets.

My Subscriber revenue widget JSON:
{
"parameters": {
"autoFitMode": "fit",
"showValues": true,
"bins": {
"breakpoints": {
"high": 100,
"low": 0
},
"bands": {
"high": {
"color": "#008000",
"label": ""
},
"low": {
"color": "#B22222",
"label": ""
},
"medium": {
"color": "#ffa500",
"label": ""
}
}
},
"legend": {
"descOrder": false,
"showHeader": true,
"show": false,
"customSize": "auto",
"position": "right-top",
"inside": false
},
"axisMode": "multi",
"tooltip": {
"showBinLabel": true,
"measures": "",
"showNullValues": true,
"showPercentage": true,
"showDimensions": true,
"showMeasures": true,
"customizeTooltip": false,
"dimensions": ""
},
"visualizationType": "hbar",
"exploreLink": true,
"title": {
"fontSize": 14,
"subtitleFontSize": 11,
"label": "Subscription Revenue",
"align": "center",
"subtitleLabel": ""
},
"binValues": false,
"trellis": {
"flipLabels": false,
"showGridLines": true,
"size": [
100,
100
],
"enable": false,
"type": "x",
"chartsPerLine": 4
},
"columnMap": {
"trellis": [],
"dimensionAxis": [
"Region"
],
"plots": [
"sum_Total_Charges"
]
},
"showActionMenu": true,
"measureAxis2": {
"sqrtScale": false,
"showTitle": true,
"showAxis": true,
"title": "",
"customDomain": {
"showDomain": false
}
},
"measureAxis1": {
"sqrtScale": false,
"showTitle": false,
"showAxis": true,
"referenceLines": [
{
"color": "#B50E03",
"label": {
"type": "dynamic",
"data": {
"step": "Attrition_Cost_1",
"sourceType": "result",
"displayTemplate": "[attrCost]"
}
},
"value": {
"type": "dynamic",
"data": {
"step": "Attrition_Cost_1",
"field": "attrCost",
"sourceType": "result"
}
}
}
],
"title": "",
"customDomain": {
"showDomain": false
}
},
"theme": "wave",
"step": "Subscription_Revenue_1",
"dimensionAxis": {
"showTitle": false,
"customSize": "auto",
"showAxis": false,
"title": "",
"icons": {
"useIcons": false,
"iconProps": {
"fit": "cover",
"column": "",
"type": "round"
}
}
},
"applyConditionalFormatting": true
},
"type": "chart"
}

My Attrition Cost Query:
"query": "q = load \"Beattie_Subs\";\nq = filter q by 'Churn' == \"Yes\" && {{row(Tenure_Length_1.selection,[0],[\"min\",\"max\"]).asRange(\"Tenure\")}};\nq = group q by all;\nq = foreach q generate count()*950 as 'attrCost';\nq = limit q 2000;",

Please suggest answer to remove this error.