I add a code that uses the following string in the functions.php file
use Google\Spreadsheet\DefaultServiceRequest;
And when I save the file it gives me an error: Parse error: syntax error, unexpected 'use' (T_USE)
I use composer and the use has to go inside the function because if I take it out, I think that's why I do not add things to the sheet.
To be able to use use or in other words "import" or "include" a class you need a namespace:
<?php
namespace foo;
use Google\Spreadsheet\DefaultServiceRequest;
The design that wordpress uses for the functions.php file does not allow to use use , since it is nothing more than a compilation of functions, without a namespace or a defined class.
You can see more information in the PHP documentation: link