UnityWebRequest change billing receipt iOS

We have a game on Unity 2019.1.10f and have a problem. When we try to buy any pack in our game (iOS platform) can be two ways: we can't buy the pack or we can get an endless loader. When we get the first way, what we do: 1. We took the receipt from Apple, sent it on our server through the native library UnityWebRequest and we saw, that the receipt, what we got before UnityWebRequest and after (in Charles) are different. It seems like the library changed our receipt, w$$anonymous$$ch we tried to send on our server for validation. 2. We take the receipt from Apple, try to send it on our server and UnityWebRequest can't send it. We don't see any requests on our server and in Charles. Who has t$$anonymous$$s problem and how we can fix it?