I was in a Duskmourn draft, and I had Dazzling Theater unlocked on the battlefield, which gives all of my creature spells convoke. I had 5 mana and a creature on board, so I attempted to cast Fear of Abduction, which is a 6 mana creature spell. However it also requires that you exile a creature you control to cast it. I thought I would be able to use the creature I had to pay for the convoke and then exile it to satisfy all the casting costs, but Arena wouldn't let me. After asking around on Discord, the consensus seemed to be that I should be able to cast the card, as I can pay both of the casting costs in whatever order I choose (rule 601.2 might apply here.)