Open Configuration
Go to Finance > Payment method
Click on +
Enter name, account and where this payment method should be used under the title “Settings”
If the payment method will be used as register payment you also need to add it to the register. Go to Configuration > Register > Registers. Click on the register where this payment method should be added.
Click on the pen next to “Payment method for registers” to add the payment method.
Click here to read more about payment methods.