When you set up Google Vacation Rentals, Guesty asks for your website link. Use this format:
https://yoursite.com/property/(PARTNER-HOTEL-ID)/?guests=(NUM-GUESTS)&checkin=(CHECKINYEAR)-(CHECKINMONTH)-(CHECKINDAY)&checkout=(CHECKOUTYEAR)-(CHECKOUTMONTH)-(CHECKOUTDAY)&pointofsale=google
PARTNER-HOTEL-ID maps to your Guesty listing ID. HomeRunner property pages accept the listing ID directly in the URL, so dates, guest count, and pricing pre-fill correctly when a guest clicks through from Google.