Bug report for "Aetherflux Reservior" in MTG Arena version 2026.58.20.12269.1265462; Brawl 29/04/26:

Opponent was able to use "Aetherflux Reservior" ability "Pay 50 life: Deal 50 damage to any target" successfully without having 50 life to pay, targeting me; resulting in them winning & my losing the match.

Their board had no life nor Artifact costs reduction excluding casting cost reduction for Artifact spells-presumably moot to using activated ability of paying 50 life

Opponent had less than 50 life; & while they were gaining life from casting various Artifact spells, they neither reached 50 life at any point during the match, nor ever had the required 50 life to pay "Aetherflux Reservior" ability "Pay 50 life: Deal 50 damage to any target"

For further details, peruse Capture log