Blockly or script - how to get sum of item since now to date

OK, what’s the nature of the date? Is it in an Item, hard coded, etc?

Try installing Date and Time which needs to be separately installed from Settings → Automation. That will

Errors in the logs? That should have worked. Looking at the code it generates a ZonedDateTime with that date and midnight as the time.

var dtf = Java.type("java.time.format.DateTimeFormatter");

var zdt = Java.type("java.time.ZonedDateTime");

function getZonedDateTime (datetime) {
  return zdt.parse(datetime + ' 00:00:00 +00:00', dtf.ofPattern('yyyy-MM-dd HH:mm:ss z'))
}

var persistence = Java.type('org.openhab.core.persistence.extensions.PersistenceExtensions');


persistence.averageSince(itemRegistry.getItem('MyItem'), getZonedDateTime('2022-03-14'));

Install the Date and Time library and use those in place of the now block. That will give you more flexibility if you need it.