Get error when assign role to user via REST API

Hi All,

I use REST API to assign role for user.
hcmRestApi/resources/11.13.18.05/userAccounts/{GUID}/child/userAccountRoles

While I use user A, it shows:

The role request couldn't be created because the  role isn't requestable. You must enter a requestable role for the user. (PER-1532349)

When I use user B, it assign correctly.

When I copy user A to a new user C, API still return error.

The URI and payload are the same.

May I know why?

Thank you,

Weitao