I don't see an "Activate" button there - instead there is a "View License" link that opens a popup with the license name and key.
These two variables should be specified for that particular OEM installation before initializing ZoomCharts:
<script type="text/javascript">
var ZoomChartsLicense = "ZCO-aaa: OEM/Redistribution licence only for use with project licence: ZCF-bbb";
var ZoomChartsLicenseKey = "2asdiv8aw39...";
var chart = new ZoomCharts.NetChart({...});
</script>