In order for Hospitable to push prices to Booking.com, a rate plan must be added to Booking.com first.
On your Hospitable properties page, if you see your Booking.com listing shows "Missing Rate Plan" 
here is how to resolve that.
On Booking.com
Log in to the Extranet
Click Rates & Availability or Calendar & Pricing and select Rate plans
Click Add new rate plan
Choose the type of rate plan you want to add, then click Add rate plan
On the next page, set up the details of your rate plan, then click Review
Click Activate rate plan
Note you may need to disconnect the Booking.com listing from us to make these changes and reconnect. If needed to do that: on Booking.com
Click on profile icon on the top right
Click on Connectivity Provider
Disconnect Hospitable there
To reconnect: Be sure to do this starting from Hospitable (not from Booking.com):
On Hospitable go to Connected Accounts
Click on Connect with Booking.com