It would probably be more easy and compact to use the Browser class in this case, see doc here with example code
EDIT : in you code you can use it like this for example :
function moveTo(e) {
// moves a row from a sheet to another when a magic value is entered in a column
// adjust the following variables to fit your needs try {
var sheetNameToWatch = "Active Discs";
var columnNumberToWatch = 15; // column A = 1, B = 2, etc.
var valueToWatch = "Completed";
var sheetNameToMoveTheRowTo = "CompletedShipped Projects";
try{
var ss = e.source;
var sheet = ss.getActiveSheet();
var range = e.range;
if (sheet.getName() == sheetNameToWatch && range.columnStart == columnNumberToWatch && e.value == valueToWatch) {
var confirm = Browser.msgBox('Do you want to move data to the other sheet ?', Browser.Buttons.YES_NO);
if(confirm!='yes'){return};// if user click NO then exit the function, else move data
var targetSheet = ss.getSheetByName(sheetNameToMoveTheRowTo);
var targetRange = targetSheet.getRange(targetSheet.getLastRow() + 1, 1);
sheet.getRange(range.getRow(), 1, 1, sheet.getLastColumn()).moveTo(targetRange);
sheet.deleteRow(range.getRow());
}
} catch (error) { Logger.log(error)}
}