Name not recognized error in List.Generate - excel

Question

I have a table with 10 columns, StepDet 1 - StepDet 10. In each one is an embedded table. I want to expand each table but not with all the columns. I only want to expand Step Name and Step 1 - 10.
I tried the below code, but I get an error that Expression.Error: The name 'prevTable' wasn't recognized. Make sure it's spelled correctly.
I would appreciate any help to move forward.
let
// Load the query
Source = Source_name,
// Generate the list of columns to expand
columnsToExpand = List.Generate(
() => [i = 1],
each [i] <= 10,
each [i = [i] + 1],
each "StepDet " & Text.From([i])
),
// Expand the columns
expandedTable = List.Last(List.Generate(
() => [i = 0, prevTable = Source],
each [i] <= List.Count(columnsToExpand)-1,
each [
i = [i] + 1,
prevTable = Table.ExpandTableColumn(
prevTable,
columnsToExpand{[i]},
{"Step Name", "ActionDet 1", "ActionDet 2", "ActionDet 3", "ActionDet 4", "ActionDet 5", "ActionDet 6", "ActionDet 7", "ActionDet 8", "ActionDet 9", "ActionDet 10"},
List.Transform(
{"Step Name", "ActionDet 1", "ActionDet 2", "ActionDet 3", "ActionDet 4", "ActionDet 5", "ActionDet 6", "ActionDet 7", "ActionDet 8", "ActionDet 9", "ActionDet 10"},
each columnsToExpand{[i]} & "." & _
)
)
],
each [prevTable]
))
in
expandedTable

Answer 1

Does something like this get you closer?
let Source = < >,
columnsToExpand = List.Transform({1 .. 10}, each "StepDet "&Text.From(_)) & {"Step Name"},
#"Unpivoted Columns" = Table.UnpivotOtherColumns(Source, List.Difference(Table.ColumnNames(Source),columnsToExpand), "Attribute", "Value"),
ColumnsToExpand = List.Distinct(List.Combine(List.Transform(Table.Column(#"Unpivoted Columns", "Value"), each if _ is table then Table.ColumnNames(_) else {}))),
#"Expanded" = Table.ExpandTableColumn(#"Unpivoted Columns", "Value",ColumnsToExpand ,ColumnsToExpand )
in #"Expanded"