To sync a listing to a channel, the system will do a validation check to ensure the listing will post without error.
The most common cause for the "Rental Agreement Required" warning/error is either the booking policy is missing a rental contract or an archived rental contract is currently applied to the booking policy being used.
To fix this error:
Step 1: Log into MyVR and navigate to Setup > Booking & Payments > Booking Policies
Step 2: Click on the booking policy being used for the listing and under the Quote Defaults section, use the Rental Contract drop-down to select a specific rental contract or select "Always Use My Default Rental Contract".
Step 3: Click Save Changes