On attack, my opponent flickered Skyclave Apparition with Ephemerate. The ETB trigger for Skyclave went off, targeting my attacking World Shaper. Despite having 1 Treasure open and Corrupted Conviction in hand, I was not given priority to sacrifice my World Shaper in response to the targeting.

The next turn, Ephemerate's Rebound resolved, and when the Skyclave Apparition triggered its ETB targeting another one of my creatures, I was given priority to sacrifice that creature to Corrupted Conviction. I had exactly the same amount of mana available in both circumstances, but was not given the ability to play my card in the first instance.