"No worthwhile reward is easily gained."
—Nicol Bolas

Font of Agonies

Whenever you pay life, put that many blood counters on this enchantment.
{1}{B}, Remove four blood counters from this enchantment: Destroy target creature.

Ravnica Allegiance Promos

Ravnica Allegiance

Whenever you pay life, put that many blood counters on Font of Agonies.
{1}{B}, Remove four blood counters from Font of Agonies: Destroy target creature.

An effect that causes you to pay life uses the word “pay.” If an effect allows you to choose to lose life or to be dealt damage without using the word “pay,” you’re not paying life.

The first ability of Font of Agonies is a triggered ability, not an activated ability. It doesn’t allow you to pay life whenever you want; rather, you need some other way of paying life, such as with Blood Crypt’s ability.