Depending on member settings, certain data fields could be connected to other required fields. If for example, the member is set to pay by credit card, and you want to edit a data field such as credit line, the platform needs to know which payment gateway to use, so it can send the credentials to the gateway or processor.
You can either select NMI or authorize.net as the payment gateway in the gateway settings section on the exchange settings screen, which should alleviate the issue. Or, you can temporarily set the member's payment profile to Other.
In any case, you'll probably want to process member fee payments from within the software to a checking account, so ideally, it's best to set-up the payment gateway and/or merchant account at the onset.
Selecting WePay for US or Canadian account settlement is ideal as it is a payment gateway + merchant account, and it gets set-up instantly with just a couple of clicks.
The Cashflow gateway is UK based (www.cashflows.com), and NMI integrates with many processors in a hundred different currencies worldwide.