It's showing both as T for me, which explains the price difference. I don't know why they aren't selling you T though
ETA: What if you click through from here:
https://flights.app.goo.gl/gLr5y
It shows me a $20 buy-up
ETA again: but when I clicked through, it said that a "real-time price change" caused my itinerary to be repriced, and it showed me G. I guess they zeroed out T? And it took a while to fully propagate?