When checking a checkbox, how to make another cell value negative?

A3 cell has a checkbox.

D3 cell has a numeric value manually entered.

What i need is to set D3 value to negative when A3 checkbox is checked.

And that behavior must repeat on all lines above line 3 (D3:D).

This is the code i am trying to line 3, but it is not working:

function onEdit(A3) {
  var ui = SpreadsheetApp.getUi();
  var sheet = SpreadsheetApp.getActive().getSheetByName('APORTES');
  var checkboxcell = "A3";
  var valuecell = "D3";
  var value = sheet.getRange(valuecell).getValue();
  var negativevalue = value*(-1);
  var type = sheet.getRange(checkboxcell).getValue();
  if (tipo="RETIRADA") {
    sheet.getRange(valuecell).setValue(negativevalue);
  }  
  if (tipo="INVESTIMENTO") {
    sheet.getRange(valuecell).setValue(value);
  }    
}