I am trying to do something similar to this How Do I Sync PR Reviewer and Jira Assignee? (atlassian.com). However instead of Assignee, I have a custom field called "Code Reviewer" (can be multiple users).
I am having a hard time setting the custom field value from the webhookData, it's expecting something like this format (I cannot pick the field from the list, so have to set it manually):
{
"fields": { "Code Reviewer": ??? }
}

I am not sure what the ??? should be, I tried many variations like this
"Code Reviewer":{{webhookData.pullrequest.reviewers.account_id.asJsonArray}} , I am also not sure webhookData is coming in as a json or xml ?