In other words the prepaid tips are not for the bar or room service. The room service you give a couple of dollars when it is brought. The bar you sign and it is added to your final bill on his sign and sail, tip included. Is it clear now? hope so?
You may pre pay your tips thur your TA either at time of booking or any time before final payment would be due. The tips amount to to $9.75 per day per person over the age of 2 years. and is broken down to wait staff $5.50, room steward $3.50 and alternate dining staff $0.75.
You can not pre pay your bar tab with the exception that you may buy bar credit cupons from Carnival's web site at gifts and services. They are sold in blocks of 4 at a cost of $19.50 and you may buy as many as you like. If you buy the cupons you must do so no later than 2 weeks before your cruise.