The OpenKJ hosting software has built in support for the Songbook service. If you're hosting with it, you will not need the Songbook Agent.
To configure it for use with the service, go to the Tools menu, then click Settings. In the settings dialog, go to the Network section.
If not already enabled, check the “Use request server” checkbox.
In the Server URL field, enter https://api.okjsongbook.com
In the API Key field, enter the API key displayed on the OpenKJ Songbook site under your account info. Make sure you don't have any leading or trailing spaces around the API key.
Click the test button. If the test is successful, you're good to go, and can close the settings dialog.
In the main interface, you will see a Requests button to the bottom right of the database pane. Click it and it will open the incoming request dialog.
Within 30 seconds of setting the API key in settings and getting a good test, the venue list should populate with your venues. If it doesn't try clicking the refresh button a couple of times to force an immediate sync with the cloud.
You can send a current copy of your song database to the cloud simply by clicking the Update Remote DB button on that dialog.
When requests come in, the Requests button on the main window will blink yellow, and optionally, you can have the requests dialog pop up automatically.