What is the ruling on the prayer of one harmed against the one who caused the accident? And does sin befall the one who caused it because of this prayer?

The mere occurrence of an unintentional mistake while driving, without intending harm, does not permit one to supplicate against a person. In fact, even against an oppressor, it is not permissible to supplicate except in proportion to their injustice, and it is better to supplicate for their guidance. The one who transgresses in his supplication will not have it answered, for Allah Almighty says: {Supplicate to your Lord humbly and privately. Indeed, He does not like aggressors} (Quran 7:55). And in the Hadith (definition): "The supplication of a servant will continue to be answered as long as he does not supplicate for a sin or the cutting off of ties of kinship." As for the value of the damage incurred by the car, it remains a liability upon you unless the rightful owner waives it. If you can reach the car owner, pay him his right or ask for his forgiveness. If you cannot, then give charity on his behalf in an amount that absolves your responsibility.