Transferring debt between credit cards within the same bank isn’t usually allowed. This will result in the bank losing money. For example, you have existing credit card debt with a lot of interest and you switch to a 0% balance transfer card with no interest. If this happened in the same bank, they would lose out on the interest they were charging. This means they might make a loss on the money you borrowed.
Therefore, if you are looking to perform a balance transfer, you will have to look at 0% balance transfer cards on offer from different banks.