As the mistake was performed because of the god Indra, he grants Hanuman a would like that his system will be as robust as Indra's Vajra, and that his Vajra also can not damage him. Coupled with Indra other gods have also granted him wishes: the God Agni granted Hanuman https://hindutempleadelaide.food.blog/2024/09/29/hanuman-mandir-south-australia-a-spiritual-and-cultural-hub/