Formula.Firewall message when I create a custom column.

Hello Anonymous 

I've checked your file now more deeply. you have 2 possibilities

Switch off the Firewall (File-> Options -> Privacy settings)

or you combine all your code in one query like that

let
    SourceCen = Excel.Workbook(File.Contents("yourExcelfileCentral"), null, true),
    RemovedColumnscen = Table.RemoveColumns(SourceCen,{"Name", "Item", "Kind", "Hidden"}),
    ExpandedDataCen = Table.ExpandTableColumn(RemovedColumnscen, "Data", {"Column1", "Column3"}, {"Column1", "Column3"}),
    PromotedHeadersCen = Table.PromoteHeaders(ExpandedDataCen, [PromoteAllScalars=true]),
    FilteredRowsCen = Table.SelectRows(PromotedHeadersCen, each true),
    RemovedDuplicatesCen = Table.Distinct(FilteredRowsCen),



    SourceDail = Excel.Workbook(File.Contents("yourExcelfileDaily"), null, true),
    RemovedColumnsDail = Table.RemoveColumns(SourceDail,{"Name", "Item", "Kind", "Hidden"}),
    ExpandedDataDail = Table.ExpandTableColumn(RemovedColumnsDail, "Data", {"Column1", "Column3"}, {"Column1", "Column3"}),
    PromotedHeadersDail = Table.PromoteHeaders(ExpandedDataDail, [PromoteAllScalars=true]),





    New = Table.NestedJoin(PromotedHeadersDail, {"URL"}, RemovedDuplicatesCen, {"URL"}, "CENTRAL_BelfastHousesBUY", JoinKind.LeftAnti),
    #"Removed Columns1" = Table.RemoveColumns(New,{"CENTRAL_BelfastHousesBUY"}),
    Page = #"Removed Columns1"[Page],
    #"Removed Duplicates" = List.Distinct(Page),
    #"Removed Bottom Items" = List.RemoveLastN(#"Removed Duplicates",1),
    #"Converted to Table" = Table.FromList(#"Removed Bottom Items", Splitter.SplitByNothing(), null, null, ExtraValues.Error),
    #"Added Custom1" = Table.AddColumn(#"Converted to Table" , "Custom", each GetDataPage([Column1]))
in
    #"Added Custom1"

If this post helps or solves your problem, please mark it as solution (to help other users find useful content and to acknowledge the work of users that helped you)
Kudoes are nice too

Have fun

Jimmy