How can I Copy/append all unique rows from SOURCE Spreadsheet to DESTINATION Spreadsheet.

• Spreadsheet #1 (SOURCE) - Contains ID's and Names. This sheet has duplicate rows. 500k+ rows (Access: View Only)
• Spreadsheet #2 (DESTINATION) - Contains only unique ID's with Names. (Access: Edit)

This script works, but it copies all (including duplicates).

function transferIDs() {
  var sss = SpreadsheetApp.openById('%'); //SOURCE
  var ss = sss.getSheetByName('Sheet1');
  var SRange = ss.getDataRange();
  var A1Range = SRange.getA1Notation();
  var SData = SRange.getValues();

  var dss = SpreadsheetApp.openById('#'); //DESTINATION
  var ds = dss.getSheetByName('Sheet1');
  ds.clear({contentsOnly: true});
  ds.getRange(A1Range).setValues(SData);
}

Spreadsheet #1 SOURCE (contains duplicate rows)

Spreadsheet #2 DESTINATION (Populated using GAS, no duplicates, Expected Outcome)