As The error was done through the god Indra, he grants Hanuman a desire that his system would be as potent as Indra's Vajra, Which his Vajra may not hurt him. Together with Indra other gods have also granted him wishes: the God Agni granted Hanuman a wish that fireplace https://hanumanjimandir.food.blog/2024/07/12/the-universal-appeal-of-lord-shanidev/