ScriptRunner Cloud cannot directly set Group Picker fields (like your customfield_10421).

[Pavan kumar Mamidipaka]

ScriptRunner Cloud cannot directly set Group Picker fields. Atlassian blocks this for security reasons — scripts can’t assign Jira groups. 

[Marc -Devoteam-]

Hi @Pavan kumar Mamidipaka 

What are your expectations around your question?

The function you want to trigger in Script runner is not allowed, as this is blocked by Atlassian.

[Amy Acker]

I ran into the same limitation while testing this.

From what I found, ScriptRunner Cloud can't directly populate Group Picker custom fields. This appears to be an Atlassian Cloud platform restriction rather than a ScriptRunner limitation, apps and scripts aren't permitted to assign Jira groups through the available API for security reasons.

[Pavan kumar Mamidipaka]

Could you please any one can suggest me