As The error was done from the god Indra, he grants Hanuman a want that his entire body could be as robust as Indra's Vajra, and that his Vajra might also not hurt him. In conjunction with Indra other gods have also granted him needs: the God Agni granted Hanuman https://hanuman-mandir-adelaide.mystrikingly.com/blog/visit-hanuman-temple-adelaide-spiritual-sanctuary-of-lord-hanuman