I am presently stuck on Einstein Analytics and Discovery Insights Specialist Superbadge (https://trailhead.salesforce.com/en/content/learn/superbadges/superbadge_analytics_insights_specialist) Challenge #3

The dashboard designer tells me there is an error in my Attrition Cost step
 

Warning! 
Analytics encountered a problem with this step [Attrition_Cost_1]. 
Input stream not found

My SAQL query is this:

beattieSubscribers = load "Beattie_Subs"; tenuredSubscribers = filter beattieSubscribers by{{row(Tenure_Length_1.selection,[0],["min","max"]).asRange ("Tenure")}}; churnedSubscribers = filter tenuredSubscribers by 'Churn' == "Yes"; attrCost = churnedSubscribers * 950.00;

What am I missing?