Пример работы с подсказками DaData.ru на Delphi

suggest.pas

function Suggest(DictionaryType, ContentType, Accept, Token, Body: string): string;
var
    IdHTTP1: TIdHTTP;
    StringStream: TStringStream;
begin
    IdHTTP1 := TIdHTTP.Create;
    StringStream := TStringStream.Create('', TEncoding.UTF8);

    try
        IdHTTP1.HTTPOptions := [hoKeepOrigProtocol,hoForceEncodeParams,hoNoProtocolErrorException,hoWantProtocolErrorContent];
        IdHTTP1.Request.ContentEncoding := 'UTF-8';
        IdHTTP1.Request.ContentType := ContentType;
        IdHTTP1.Request.Accept := Accept;

        IdHTTP1.Request.CustomHeaders.Add('Authorization: Token ' + Token);
        StringStream.WriteString(Body);

        Url := 'https://suggestions.dadata.ru/suggestions/api/4_1/rs/suggest/' + DictionaryType;
        Result := IdHTTP1.Post(Url, StringStream);
    finally
        StringStream.Free;
        IdHTTP1.Free;
    end;
end;

procedure TForm1.Button1Click(Sender: TObject);
var
    DictionaryType: string;
    ContentType: string;
    Accept: string;
    Token: string;
    Body: string;
begin
    DictionaryType := 'party';
    ContentType := 'application/json';
    Accept := 'application/json';
    Token := '***';
    Body := '5408110390';
    Memo1.Text := Suggest(DictionaryType, ContentType, Accept, Token, Body)
end;