Same thing happened to me about trying to use an RUC when the agent insisted I had to use a GUC. It was an international plane, ATL - SEA, so of course that is not D1, but agent said otherwise, regardless of what the website said. I asked her to check with a supervisor, and they made “a one time exception for me…”. None of this needs to be complicated, but Delta feels otherwise. But the fact that they doubled down that it was an exception was ridiculous. I filed a complaint online and suggested that if they want me to have to train their agents, they will need to start paying my hourly rate…