TNR-2190: Fix validation issue with adding reservation guests (#34)

* TNR-2190: Fix validation issue with adding reservation guests

Also sneak in `initial_payment_amount` because I already had it there.

* Update vacasa/connect/connect.py

Co-Authored-By: bijan-vacasa <33635269+bijan-vacasa@users.noreply.github.com>

Author: bijan-vacasa

vacasa/connect/connect.py

@@ -664,6 +664,7 @@ def create_reservation(self,
                            trip_protection: Optional[bool] = None,
                            source: Optional[str] = None,
                            discount_id: Optional[int] = None,
+                           initial_payment_amount: [float] = None
                            ) -> dict:
         """ Reserve a given unit
 
@@ -695,6 +696,8 @@ def create_reservation(self,
             cvv: Card verification value on credit card
             source: A Vacasa-issued code identifying the source of this request
             discount_id: Must match value from `quote_id`
+            initial_payment_amount: if included, only process this amount initially, the remaining balance will be
+                                    charged according to payment plan logic (i.e. 30 days before check-in)
 
         Returns: dict
 
@@ -736,6 +739,9 @@ def create_reservation(self,
         if discount_id:
             payload['discount_id'] = discount_id
 
+        if initial_payment_amount:
+            payload['initial_payment_amount'] = initial_payment_amount
+
         return self._post(url, json={'data': {'attributes': payload}}, headers=headers).json()
 
     def create_cancelled_reservation(self,
@@ -890,7 +896,8 @@ def add_reservation_guests(self,
             'email': email
         }
 
-        return self._post(url, json={'data': {'attributes': payload}}, headers=headers).json()
+        return self._post(url, json={'data': {'attributes': payload,
+                                              'type': 'reservation-guest'}}, headers=headers).json()
 
 
 def _handle_http_exceptions(response):