File downloading with PHP Rest API [closed]

I'm developing a rest API with PHP. I capture the posted data and prepare an Excel output after the transactions in the database. I can save the Excel output to the server where PHP is installed, but I don't know how to send the file to the client via Rest API. A simple code example will do the trick for a start. I request your support.

case "ProcessClicheExport":{   /// ..... file creation process (.xlsx)   $writer = new Xlsx($spreadsheet);   $writer->save('Test.xlsx');/// ..... What should I write in this field for response?   break;}