Unfortunately after a few weeks of discussions with support, it looks as though you do not support Yorkshire Business Bank Accounts.
Their accounts require authentication by the mobile app. When attempting to use the Cylesdale and Yorkshire option, it errors straight with 103. The mobile app does not signal that authentication is required. The other option available in the list is Yorkshire, but this does not enable you to enter a User ID.
I hope others see this that may end up in the same situation.