A balance transfer is essentially asking one bank or issuer to pay off part or all of your debt to another. That’s why you cannot do a balance transfer from one card to another if the same financial institution issues both cards. If you request a balance transfer within the same bank, it will be denied.
Another reason that a balance transfer could be denied is if you do not have enough available credit to cover the amount you have requested to transfer. This could happen if you request a balance transfer at the same time you apply for a new card – something many cards allow you to do.
For example, you might apply for a card and put in a request for a balance transfer of $8,000, but only be approved for a new card with a credit limit of $5,000. In this case, the request will either be denied, or it will go through for the lesser amount of $5,000. Different issuers have different policies about this, so check the terms and conditions when you apply for a new card if you are planning to do this.
As long as you are requesting a transfer from one financial institution to another and you have enough available credit to make the transfer, there is no foreseeable reason that the balance transfer would be denied.