Step #1:
Log into your Checkbook.io account.
Step #2:
In the menu on the left, choose "Send Payment"

Step #3:
Fill out the payment information and then click the Direct Deposit button.

Step #4:

When you see this window, enter the Routing Number that is associated with your recipient's bank account.
Under the “Account number” & “Confirm account number” prompts, enter your recipient's Bank Account Number. Please take an additional step to ensure that the account number is accurately typed in.
Then proceed to "Account Type" and select one of the three options that indicates your recipient's bank account type.

Once a selection is made, click “Confirm & Send Payment”