How to resolve issue in automation rule to sum up Story points estimate ?

[Karthieswari Baskar]

I have configured the below rule to sum the story point estimate of the subtasks 

I also tried below variations.

{
  "fields": {
    "Story point estimate": {{#=}} {{subtasks.Story point estimate.join(" + ") }} {{/}}
  }
}

or

{
  "fields": {
    "Story point estimate": {{#=}} {{#subtasks}} {{Story point estimate}} + {{/}} 0 {{/}}
  }
}

 But I have the following error, did anyone face similar issue and know how to resolve ?