Gas: Calculate Magnitude not working

Hello.
I trying using GAS for my rpg project. and I try to implement simple damage system. But I see warning in my log “LogAbilitySystem: Warning: Modifier on spec: Default__SimpleDamageGameplayEffect_C was asked to CalculateMagnitude and failed, falling back to 0.” and damage reset to 0.

How its suppose to work: Ability Instant add to enemy health value, calculated from Attribute Damage of my attacking actor. It has -1 coefficient because I want to decrease value, not increase, and use Source Attribute Damage from caster.
This Attribute definitly exist in caster, but this does not work.
This Effect work, when I use scalable float or curve table.
Where is my mistake?

For anyone who google and found my question: you should use ApplyGameplayEffectToTarget functiuon

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