I had an Essence Channeler and a Starting Town. I went to my declare attackers step before tapping Starting Town. Regardless of whether I actually have anything to pay for with the mana, I should be able to use the Starting Town to add one mana of any color to my mana pool and paying 1 life and giving my Essence Channeler Flying and Vigilance. But during the game, 1. I was unable to activate abilities during my declare attackers, and 2. also did not receive priority before the declare blockers step so I had no chance to give my essence channeler flying. This is not consistent with the official MTG rules.