Energy Safety found the machine had no voltage markings, it was not earthed and had only basic insulation of exposed metal parts.
Spokesman for WorkSafe New Zealand Brett Murray said the 439 bubble machines GrabOne sold were unsafe.
"These machines were simply unsafe. They did not provide adequate protection from contact with live parts ? and there was little separation between the water used to make bubbles and live electrical components.
"This is the first time an online marketplace has been charged as a party to this type of offending. They are more than just a sales venue and are responsible for the actions of merchants that use them.
"GrabOne had a duty to ensure they were safe to use."
Tracey Moerkerk, Operations Director for GrabOne, said in a statement: "We acknowledged from the beginning we got this wrong which is why we pleaded guilty. While the situation is highly regrettable we are confident we have improved our systems so that this situation would not happen again."