RT 4.4.2 + REST API + show Custom Role

RT Users
1

I created Custom Role “ProductOwners” (multivalue).
I created ticket #123 and entered two users in this role.
How can I show this field using REST API?
I tried:
/REST/1.0/search/ticket?query=id=123&format=l&fields=CC,CR.{ProductOwners}
Result:

RT/4.4.2 200 Ok

id: ticket/123
Cc: some.user@contoso.com

also tried:
/REST/1.0/search/ticket?query=id=123&format=l&fields=CC,ProductOwners
with no luck.

I tried:
/REST/1.0/ticket/123/show
Result:

RT/4.4.2 200 Ok

id: ticket/123
Queue: <queue>
#and other information without ProductOwners custom role
2

As far as I know, you can’t do this with REST1, only with REST2, which you need to setup manually.