I have seen several posts about this issue but I still haven't been able to get it to work.
We're on JIRA Cloud
Company Managed Project
I tried 2 different solutions, neither of which worked.
Here is the first (didn't have room to capture the entire screen but the first steps is the one at the right "Field Value Changed")

Here is the second one I tried

In the story points field I used
{{lookupissues.Story Points.sum}}
Any help would be greatly appreciated.