1. Login to Online Check Writer and select Apps.
2. Click ClearBooks and click Connect.
3. Click Continue.
4. Enter your ClearBooks API key; you get the API from the ClearBook account’s settings: open the ClearBooks account, go to Settings, click Configure System, and click API keys. Then you can see your API key as SOAP API.
5. Click Submit; then the window will show a message like “Connected to ClearBooks.”
6. Click on Continue.
7. Then, click on Finish.

To import invoices from ClearBooks, 

1. Go to Invoice in the Receivables bar.
2. Click Import Invoices and select ClearBooks.
3. Choose the company and update Import Settings: select Time Span and Download Filter.
4. Click Start Importing.