Miles witnessed John drive through a red light while on his cell phone and hit another vehicle.

Miles witnessed John drive through a red light while on his cell phone and hit another vehicle. John approached Miles and offered him $500 to offer a witness statement saying he hadn't seen John drive through the light. Miles agreed. John gave him $100 but then never gave him the rest of the promised money. Miles would like to sue John for breach of contract. What issues arise in this scenario?