Unable to add user to the administrators project role via jira plugin code

Please help me to provide a resolution for the below issue. Appreciate your quick feedback. Thanks in advance.

User should be added “ Administrators ” Project Role via JIRA Plugin Code

Detailed description of the issue
I am developing JIRA Plugin to add user to the “Administrators” Project Role via JIRA Plugin.
Plugin failed to perform this functionality for few users (for other users, it works well) & returned the error message “ We can’t find the ‘user’ in any accessible user directly. Check if they are still available & active and try again. ” However, I can add the same user via JIRA UI and JIRA REST API without any issue. Please find the code snippet below as reference.

ProjectRoleManager projectRoleManager = ComponentAccessor.getComponent(ProjectRoleManager.class);

ProjectRoleService projectRoleService = ComponentAccessor.getComponent(ProjectRoleService.class);

ProjectRole projectRole = projectRoleManager.getProjectRole(“Administrators”);
ArrayList actors = new ArrayList<>();

ErrorCollection errorCollection = new SimpleErrorCollection();
projectRoleService.addActorsToProjectRole(user, (Collection)actors, projectRole , project, ProjectRoleActor.USER_ROLE_ACTOR_TYPE, errorCollection);

return “Failed to add user !!”;
return “Successfully added user”;

Diagnostic Steps

I have followed these steps to verify this issue

  1. Verified JIRA DB to check if there is any trailing space/blank space for that user. But no such extra space available.
  2. User can be added to the “Administrators” role via JIRA UI manually
  3. User can be added to the “Administrators” role via JIRA REST API