public async Task<byte[]> RenderExcelAsync(string exceltemplate, object exceldata, string excelhelperFunctions = null)
        {
            try
            {
                Template excelt = new Template()
                {
                    Engine = Engine.Handlebars,
                    Recipe = Recipe.Xlsx,
                    Content = "{{{xlsxPrint}}}",
                    Xlsx = new Xlsx()
                    {
                        TemplateAsset = new Asset() { Encoding = "base64", Content = exceltemplate }
                    }
                };

                if (!string.IsNullOrEmpty(excelhelperFunctions))
                    excelt.Helpers = excelhelperFunctions;

                RenderRequest req = new RenderRequest()
                {
                    Template = excelt,
                    Data = exceldata
                };
                var result = await _service.RenderAsync(req);

                if (result.Content != null)
                {
                    using (var memoryStream = new MemoryStream())
                    {
                        result.Content.CopyTo(memoryStream);
                        return memoryStream.ToArray();
                    }
                }
                else
                    throw new ApplicationException("There was an error generating the PDF file.");
            }
            catch (Exception)
            {
                throw;
            }
        }
    }

it runs but instead of returning the rendered document it returns the template basically

it keeps returning the template instead of the rendered document

Do you mean it returns xlsx file, but the original exceltemplate template without changed cells?
This would be expected, because you provide no calls here Content = "{{{xlsxPrint}}}",