As the error was completed from the god Indra, he grants Hanuman a want that his body would be as robust as Indra's Vajra, and that his Vajra can also not harm him. Along with Indra other gods have also granted him wishes: the God Agni granted Hanuman a wish https://medium.com/@HinduTempleAdelaide/hanuman-mandir-and-shani-dev-temple-adelaides-premier-hindu-sites-7150c2cd1421?postPublishedType=initial