The flow is the same for all AffiniPay payment solutions (ClientPay/DesignPay, LawPay, CPACharge, and AffiniPay for Associations). You need to set up an ePayments profile in Global Settings > ePayments by choosing one of these payment solutions and type, and then signing in through that payment account. You can also sign up for a new account if you do not have one. Core recommends that you choose a solution that matches your industry type. After that, you need to configure the ePayments settings to complete the profile. You can then select the ePayments profile you created as the online payment account at the client, project, or invoice level. Check out this FAQ for all the details: How do I set up AffiniPay ePayments in Core.