They are asking for a pic of receipt,so they can narrow down a massive,massive field of models,and find a supplier to make sure issue doesn't affect a batch of models.They want to know you purchased the model,and it left the factory,damaged/piece missing,whatever.Otherwise it coud have changed hands many times before and been damaged,along the way.They have been making models for over 40 years,so there are literally,zillions out there.