Jira Automation to append several email/account custom fields to Request Participants

[melissa_cheney]

I have several automations that take an email custom fields, verify account ID and put them in the Request Participants. Here is the JSON code: 

{ "update": { "Request participants": [{ "add": {"id":"{{webresponse.body.accountid}}"} }] } }

My issue is each automation overwrites the existing Request Participants and does not append. What do I need to change in my JSON so it just appends the list?