fix: enhance phone number validation to check for unsupported country codes

Author: andrewleith

notifications_utils/recipients.py

@@ -505,9 +505,14 @@ def validate_phone_number(number, column=None, international=False):
     if len(number) < 8:
         raise InvalidPhoneError("Not enough digits")
 
-    if get_international_prefix(number) is None:
+    prefix = get_international_prefix(number)
+    if prefix is None:
         raise InvalidPhoneError("Not a valid country prefix")
 
+    # if the prefix is not in our billing rates, then we don't send to it, so we should error here
+    if INTERNATIONAL_BILLING_RATES.get(prefix) is None:
+        raise InvalidPhoneError("Country code {} is not supported".format(prefix))
+
     return number