The official rule should be $10 per guest per day up to 2 guests. In some destinations, it may cover breakfast or almost cover it (so in a few cases hotels just let you use the credit for that rather than calculating the difference in local currency). For others you need to pay for breakfast then minus the credits off the bill. The price is usually cheaper if you tell them the night before you’re having breakfast. Some hotels didn’t have this requirement of giving notice for the lower price if you’re a member. You could just tell them that morning and be charged the cheaper price. Check with each specific hotels for their exact policy.