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 the product is factory calibrated to meet the accuracy requirements, but not certified, of a Class B active electrical energy meter as written in 2014/32/EU (MID) Annex V, and implemented in EN 50470-1:2006 and EN 50470-3:2006.
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%.