Just like an applicant can get on a single autobilling plan, here you can decide activate the ability to be on multiple plans simultaneously.
To adjust this setting, first make sure you are on the Autobilling page. Navigate to the "Settings" drop-down menu, and select "Autobilling".
Click tools at the top of the page, and then click general autobill settings
Click the toggle next to “Allow users to be on multiple plans” to toggle it “on”
Make sure to click save once you are done!