Split Column IF condition in another column is true

[ilcaa]

i am trying to split a column if the condition are true in another column. i keep getting errors in my M Code

let
    Source = Csv.Document(File.Contents("C:\Users\MTS\Documents\Activity Dec 2018.csv"),[Delimiter=",", Columns=7, Encoding=1252, QuoteStyle=QuoteStyle.None]),
    #"Promoted Headers" = Table.PromoteHeaders(Source, [PromoteAllScalars=true]),
    
    #"Split Column by Position" = Table.SplitColumn(#"Promoted Headers", "Description",  each if [Type] = "BILLPAY" then Splitter.SplitTextByPositions({0, 29}, false) else null, {"Description.1", "Description.2"} )
           
    
in
     #"Split Column by Position"