If the instruction to Pay resources is part of paying costs for a card or ability, choosing not to pay those resources will cause the act of playing the card or ability to be undone. See rule 358. Check Legality for more information.
§ 444.2.a Core Rules PDF (officieel)
§ 444 Pay
§ 444.2 When a player is instructed to Pay a resource, that player may remove that resource from their Rune Pool if it exists there. If they choose not to, the instruction is ignored. Example: When Diana, Lunari’s triggered ability resolves, if its controller has [1] Energy in their rune pool, they choose w…
