In Telegram API type UserProfilePhotos has field photos which is Array of Array of PhotoSize(https://core.telegram.org/bots/api#userprofilephotos).
Your Java class UserProfilePhotos field photos has type List<PhotoSize>, so when you get response from Telegram API there is an error of parsing JSON. I have changed type of the field photos to List<List<PhotoSize>>, which solved the problem.
In Telegram API type UserProfilePhotos has field photos which is Array of Array of PhotoSize(https://core.telegram.org/bots/api#userprofilephotos). Your Java class UserProfilePhotos field photos has type
List<PhotoSize>, so when you get response from Telegram API there is an error of parsing JSON. I have changed type of the field photos toList<List<PhotoSize>>, which solved the problem.