As the mistake was done because of the god Indra, he grants Hanuman a wish that his physique will be as powerful as Indra's Vajra, Which his Vajra could also not harm him. Along with Indra other gods have also granted him wishes: the God Agni granted Hanuman a desire https://indianhindutempleadelaide.blogspot.com/2024/07/a-deeper-dive-into-hanuman-mandir.html