QZ Tray — install from qz.io/download, then leave it running (Mac menu bar / Windows tray).
Seller Desk — Add to Chrome from the Web Store. Pin it → Open desk. If you still have the old unpacked zip, remove that card first.
Key — open the desk from the extension → paste the key → Save.
Printer — Find printers → pick iDPRT or Polano → Test print. The first QZ dialogs should say Verified by QZ Industries. Check Remember this decision on both (find printers and print), then Allow. After that, labels stay silent until QZ is quit.