Strong Customer Authentication is a requirement rolled out across Europe by the EU Revised Directive on Payment Services (PSD2). It requires a multi-factor authentication for electronic payments in order to increase its security and prevent fraud. This can be something the customer knows (password/pin), something the customer has (phone/hardware token) or something the customer is (fingerprint or face recognition). Most card payments and all bank transfers will require SCA in the future. In the UK it will be enforced over the course of 2021.
When you initiate a payment in CashFlow Manager you are being redirected to your banking app where you will most likely need to perform SCA to complete the payment giving you further protection.