To sign into Banking Circle, you need to go through Strong Customer Authentication (SCA) by following the steps below. SCA is a requirement under PSD2.
Download the Authy app to your mobile phone (available through App Store and Google Play) or desktop app (available from authy.com)
Setup Authy according to the details found in your Welcome e-mail
When making payments to new/unsaved creditors, the payment will need to be authenticated under SCA by using the Authy app.
Authentication under SCA is also required when creating a new creditor or making changes to recurring payments.