assignment complete from plugin is does not work

I try to complete assignment from plugin but doesnt work.

ApplicationContext applicationContext = AppUtil.getApplicationContext();
        WorkflowManager workflowManager = (WorkflowManager) applicationContext.getBean("workflowManager");
ApplicationContext applicationContext = AppUtil.getApplicationContext();

WorkflowManager workflowManager = (WorkflowManager) applicationContext.getBean("workflowManager");

workflowManager.assignmentComplete("197_61_complain_complain_raiseIssue");

any suggestion?