When do you need to pay the deflect cost when targeting a unit with deflect using a unit ability like Ezreal Dashing - when putting it on the chain or when resolving?

Ruling: Deflect costs are paid when the ability is put on the chain, not when resolving.

Nuances:

• For abilities that don't target (like red Draven), costs may be paid during resolution rather than when putting the ability on the chain - this depends on the ability's layout, not whether it targets
• Deflect is not an optional additional cost, so it cannot be paid using abilities that allow paying optional additional costs