If being trained to use pads is your long term goal you can increase your chances and minimize the time it will take by having them in their crate/pen as much as possible to create the opportunity for praise. Training a puppy to go outdoors is easier in some respects since there is a lot of room in which going potty is okay and there are things for you and your puppy to do while waiting for the right time. When pad training you have to rely on having the pad/tray within sight of the puppy most of the time since there is nothing else to occupy the puppy while he is waiting for the need to arise.
I am not sure wether your goal is outdoor or indoor training, if it is outdoor you are off to a great start since he likes going out there. If you wish to have him use the pad then he first must spend as much time as possible in his palace for the first week or two to learn that it is okay to eliminate there. You then increase his available are by adding an exercise pen attached to the palace or placing the palace in a small room such as a bathroom with the palace door open for a couple weeks. Then you can give him access to larger areas of your house but still take the pad/tray with you.
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