If you do not use online banking, The Closing Docs is unable to verify your income. The Closing Docs works by connecting to your online banking account in order to collect deposit history.
Under these circumstances, you can click the "What if my bank is not supported" link and write in that you do not have a bank or do not use online banking. This will send a notice to your decision maker and prompt them to verify your income in other ways, such as with pay stubs or bank statements.
The link "What if my bank is not supported" only appears if you have started the process. So, in order to notify your decision maker, you must start the automated income verification process and let them know you do not use a bank.