Create a hotel booking and get the payment link

Guests per room (title, first_name, last_name, age; is_child for children), the contact (email, phone) and optional special_requests (requests[] from early_checkin, late_checkout, high_floor, quiet_room, non_smoking; bed any|king|twin; notes up to 200 characters, forwarded to the hotel and subject to availability). Returns the booking reference and a one-time payment_url valid for payment_expires_in seconds; the customer pays and accepts the terms on that page.