You can block or disable payments made to your account without disconnecting your payment gateways. 

To Disable online payments:

1. Begin in your dashboard and navigate to Settings > Payments.
2. Scroll to the bottom of the page and uncheck the online payment options.
3. Click Save at the top of the page to save your changes.

If an online payment is attempted, the client will get this error screen:

A new client is still captured and added to your Clients list as a lead.