Auto Pay does not use Galazeth Prizmari's ability to pay X costs.
Issue: When casting spells with X in the mana cost, Auto Pay will ignore non-treasure artifacts, and will sacrifice treasures rather than tap them, to pay the additional mana cost for X.
Context: Galazeth Prizmari's passive ability allows his controller to tap artifacts for one mana of any color. If some of the artifacts in question are treasures, this is usually the better choice, rather than sacrificing treasures for the same one mana of any color.
Steps To Reproduce: Start a match using the Galazeth Prizmari deck, featured in the Perfectly Normal Event.
Spend turns 1-3 amassing artifacts on-board and Instants and Sorceries in-hand.
Turn 4, cast commander.
Turn 5, cast an X spell for the highest amount you can afford by tapping all artifacts. Tap all non-treasure artifacts, so that the Auto-pay button appears. Press Auto-Pay. Observe that all treasures that should have been tapped are sacrificed.
Why this matters: Players must spend timeouts and bore the opponent, manually tapping each artifact, which may not be feasible in Arena for costs of 8 or more. Since repeatedly casting abnormally large X spells is the main advantage of this commander, failing to tap for the mana in time can result in a string of frustrating, unearned defeats. Galazeth Prizmari is normally fun and rewarding to play even in defeat, and Arena is completely failing to do this card justice.