Hi,
I've got a Custom Field called Allow Users. I'd like to add users into it via Post Function in Workflow. Adding current user with variable %%CURRENT_USER%% works, but I don't know what is the syntax to add other users.

I've tried to add user accountId like "12k23421ll232" from URL https://admin.atlassian.com/s/instanceID/users/12k23421ll232
Separated with space, comma, semicolon, new line.
There's error Unable to update custom field customfield_10045 - Allow Users in issue [DIT-56]. when I try to transition the issue when the syntax is wrong.
Does somebody know the syntax?
Cheers,
Juho