Cash deposits to NatWest accounts will clear instantly, and all other transactions will be processed in the same timescales as if paid in at the branch counter. Natwest and Royal Bank of Scotland customers can use CDMs at either NatWest or Royal Bank of Scotland branches regardless of their home brand.
In case of a transaction failure, ISHS recommends to first try using an alternative credit card, or to give it another try with the same credit card again but at a later time. In most cases this would solve the issue. Do carefully check the card details before confirming the transaction for processing.