google apps script - Custom function throws a "You do not have the permission required to setValue" error

Question

I am trying to set some value to a cell in a Google Spreadsheet:

    function exampleFunction() {
      var ss = SpreadsheetApp.getActiveSpreadsheet();
      var sheet = ss.getSheets()[0];
      var range1 = sheet.getRange("A1");
      var value1 = range1.getValue();
      value1+=1;
      range1.setValue(2);
      return value1;
    }

If I am trying to affect a cell with this function, this error appears:

You do not have the permission required to setValue. (line 10, file "ddd")

Do you know how I could make that possible? I actually want the affected cell to take the value of the cell A1 and increase the value of A1 by 1.

Answer 1

from the documentation :

Custom functions return values, but they cannot set values outside the cells they are in. In most circumstances, a custom function in cell A1 cannot modify cell A5. However, if a custom function returns a double array, the results overflow the cell containing the function and fill the cells below and to the right of the cell containing the custom function. You can test this with a custom function containing return [[1,2],[3,4]];.

reference : Custom Functions in Spreadsheets