The metering accuracy of your Zaptec Go depends on whether it has been factory-calibrated. You can check this by looking at the product label on the underside of the charger.
If the product label article number is 820-00024 then the internal energy meter has been factory calibrated to MID Class B accuracy, which is +/- 1%. You can download the calibration declaration via the link at the bottom of this article.
If the article number is not 820-00024, then your charger has been manufactured with a metering accuracy of +/- 3%.