Hello,
I have scanned all post about summing up Epic's tasks and still didn't find solution to my problem - while changing "Story points" value on child task, rule executes and show that did the modification but nothing is actually changing in Epic (parent) task.
Funny thing is, that for my other JIRA account (other Client), both solutions are working.
I used that one: for editing field: {{lookupIssues.Story Points.sum|0}}


I also took another recommended approach - still not working:

Any idea?