- Spend refers to any ability that allows a player to choose to pay gold (e.g. marshalling a card or playing an event) or move gold (e.g. bestow) from their gold pool. (Source)
During the marshaling phase, you may spend gold on The Iron Bank as if it were in your gold pool.
Reaction: After you collect income, move X gold from the treasury to The Iron Bank. X is the number of gold on The Iron Bank.