As the error was done by the god Indra, he grants Hanuman a want that his system would be as robust as Indra's Vajra, and that his Vajra might also not hurt him. Together with Indra other gods have also granted him wishes: the God Agni granted Hanuman a wish https://elizabethy862lor3.blogdomago.com/35822838/facts-about-hanuman-revealed