Combine two tables based on date ranges.

Anonymous make sure you use correct dates (you have 31st of April in your data). Also make sure you have dates in rates table earlier than min date in GL table. Replace your_rates_table and your_GL_table in code below with correct references to your tables.

let
    // this is your table with rates. Had to trim ccy column later.
    s_rates = your_rates_table,
    date_type = Table.TransformColumnTypes(s_rates, {{"Effective Date", type date}}, "en-AU"),
    trimmed = Table.TransformColumns(date_type,{{"From Currency", Text.Trim, type text}}),
    // this is your table with amounts
    before = your_GL_table,
    b_type = Table.TransformColumnTypes(before, {{"GL Date", type date}}, "en-AU"),
    // make a record with ccy name fields and list of dates and rates sorted by date
    rates = 
        Table.Group(
            trimmed, "From Currency", 
            {{"rates", each List.Sort( List.Zip({_[Effective Date], _[Multiplier]}), {(x) => x{0}, Order.Descending})}}
        ),
    rec = Record.FromList(rates[rates], rates[From Currency]),
    // add Multiplier column.
    after = 
        Table.AddColumn(
            b_type, "Multiplier",
            each [a = Record.FieldOrDefault(rec, [Base Currency], null),
            b = a{List.PositionOf(a, [GL Date], Occurrence.First, (x, y) => x{0} <= y)},
            c = if b = -1 then null else b{1}][c]
        )
in
    after