Use case
Return the result of summing the multiplication of the field values of two Number fields in every sub-task of the current issue.
Expression
Create and configure a Smart field using this expression in Jira expression mode:
issue.subtasks.length && issue.subtasks.map( s => (s.customfield_nnnnn || 0) * (s.customfield_ppppp || 0)).reduce((a, b) => a + b)
Please, replace nnnnn and ppppp in the above expression with the IDs of the Number fields.
