As the error was done via the god Indra, he grants Hanuman a wish that his system will be as powerful as Indra's Vajra, and that his Vajra also can not harm him. Together with Indra other gods have also granted him needs: the God Agni granted Hanuman a desire https://indianhindutempleadelaide.blogspot.com/2024/08/hanuman-jayanti-2025-at-hanuman-mandir.html