I have a Google Pixel XL and it says that sending 'premium texts and picture messages' are part of my plan. I can receive pictures, but when I try to send it, it says "Not sent. Tap to try again". I've had this phone for over a year now so I know it has nothing to do with having to reset my phone or screw around in my settings (as far as I know). My brother has the exact same phone and he has no issue sending picture messages and gifs my way. I also had a Samsung phone with the same problem.