Build an Excel FX tracker with Gemini and Power Query

Write a macro-free Excel Power Query M query that calls
https://exchangerate.dev/docs/api-reference
and the anonymous endpoint /v1/latest/USD?symbols=JPY,KRW,EUR.
Use Web.Contents with RelativePath = "v1/latest/USD" and
Query = [symbols = "JPY,KRW,EUR"]. Parse the JSON response,
validate that rates, sources, data_updated_at, and market_session
exist, then return columns Currency, Rate, Source,
DataUpdatedAt, and MarketSession. Do not add an API key or
invent fallback values. Keep HTTP errors visible.

let
    Response = Web.Contents(
        "https://api.exchangerate.dev",
        [
            RelativePath = "v1/latest/USD",
            Query = [symbols = "JPY,KRW,EUR"],
            ManualStatusHandling = {429}
        ]
    ),
    Status = try Value.Metadata(Response)[Response.Status] otherwise 200,
    Checked = if Status <> 200 then
        error "The FX endpoint returned HTTP " & Text.From(Status)
      else Response,
    Json = Json.Document(Checked),
    Rates = try Json[rates] otherwise error "The response has no rates field",
    Sources = try Json[sources] otherwise error "The response has no sources field",
    UpdatedAt = try Json[data_updated_at] otherwise error "The response has no data_updated_at field",
    Session = try Json[market_session] otherwise error "The response has no market_session field",
    RequireRate = (rates as record, code as text) as number =>
        let value = try Record.Field(rates, code) otherwise null
        in if value is number and value > 0 then value else error (code & " is missing or invalid"),
    RequireSource = (sources as record, code as text) as text =>
        let value = try Record.Field(sources, code) otherwise null
        in if value is text and Text.Length(value) > 0 then value else error (code & " source is missing or invalid"),
    RequiredMetadata = if UpdatedAt is text and Text.Length(UpdatedAt) > 0 and Session is text and Text.Length(Session) > 0 then true else error "Required metadata is missing or invalid",
    Rows = if RequiredMetadata then Table.FromRecords({
        [Currency = "JPY", Rate = RequireRate(Rates, "JPY"), Source = RequireSource(Sources, "JPY"), DataUpdatedAt = UpdatedAt, MarketSession = Session],
        [Currency = "KRW", Rate = RequireRate(Rates, "KRW"), Source = RequireSource(Sources, "KRW"), DataUpdatedAt = UpdatedAt, MarketSession = Session],
        [Currency = "EUR", Rate = RequireRate(Rates, "EUR"), Source = RequireSource(Sources, "EUR"), DataUpdatedAt = UpdatedAt, MarketSession = Session]
    }) else error "Required metadata is missing or invalid",
    Typed = Table.TransformColumnTypes(Rows, {{"Currency", type text}, {"Rate", type number}, {"Source", type text}, {"DataUpdatedAt", type datetimezone}, {"MarketSession", type text}})
in
    Typed