The most common reason that Uplisting is not syncing with Booking.com (BDC) is that the connection is not completed on Uplisting or BDC.
Ensure the connection is confirmed on BDC
This is the #1 reason bookings aren't importing to Uplisting, and rates and availabilities aren't syncing from Uplisting to BDC.
How to fix it
Typically you have one final step on the BDC channel manager page to confirm Uplisting as your channel manager. Ensure you are in Step 5 on the channel manager extranet page
1. Go to your BDC extranet, channel manager page
2. Select 'confirm the connection with provider'
Once you select that (it moves from step 4 to step 5) Uplisting will sync availability and rates to BDC within 20 mins. If your listing is closed due to availability (it may not be) it should then open automatically.
Ensure the connection is established on Uplisting
On Uplisting make sure you have matched the listing(s) and confirmed the connection on the listings BDC settings area.
If neither of those are the issue let me know and we'll take a look for you.