Authorize.net CIM
The Authorize.Net Customer Information Manager (CIM) allows you to store customers' sensitive payment information on our secure servers, simplifying your compliance with PCI regulations whilst still enabling clients to enter their card details directly onto your website and processing recurring payments.
Usage
Begin by activating the Authorize.net CIM module in Setup > Payment Gateways and then enter your Auth.net Login ID & Transaction Key where requested.
Contrary to what you might think, you should not tick the setting to "Disable Credit Card Storage" in Setup > General Settings > Security as that will disable entry by a client.
It must be enabled to show the credit card payment form and allow clients to update their card details, but the fact you are using the Authorize.net CIM module will prevent the details being stored locally in WHMCS and instead store them only on the remote system.
In order for the credit card details to be sent to the CIM the client must first make an initial payment manually via the client area. A client profile is then created at the CIM storing the card details allowing subsequent invoices to take payment automatically. The significance of this is that card details cannot be entered via the admin area.
Validation Mode
The Validation Mode parameter enables you to generate a test transaction at the time you create or update a customer profile.
Live — Generates a transaction to the processor in the amount of $0.01 or $0.00. If successful, the transaction is immediately voided. Visa authorization transactions are changing from $0.01 to $0.00 for all processors. All other credit card types use $0.01. Consult your Merchant Account Provider before changing to Zero Dollar Authorizations for Visa because you may be subject to fees.
None — When this value is selected, no additional validation is performed.