This field must be empty for the first address validation request. If more requests are necessary to fully validate a single address (for example if the changes the user makes after the initial validation need to be re-validated), then each followup request must populate this field with the response_id from the very first response in the validation sequence.

Enables USPS CASS compatible mode. This affects only the [google.maps.addressvalidation.v1.ValidationResult.usps_data] field of [google.maps.addressvalidation.v1.ValidationResult]. Note: for USPS CASS enabled requests for addresses in Puerto Rico, a [google.type.PostalAddress.region_code] of the address must be provided as "PR", or an [google.type.PostalAddress.administrative_area] of the address must be provided as "Puerto Rico" (case-insensitive) or "PR". It's recommended to use a componentized address, or alternatively specify at least two [google.type.PostalAddress.address_lines] where the first line contains the street number and name and the second line contains the city, state, and zip code.

Optional. A string which identifies an Autocomplete session for billing purposes. Must be a URL and filename safe base64 string with at most 36 ASCII characters in length. Otherwise an INVALID_ARGUMENT error is returned. The session begins when the user makes an Autocomplete query, and concludes when they select a place and a call to Place Details or Address Validation is made. Each session can have multiple Autocomplete queries, followed by one Place Details or Address Validation request. The credentials used for each request within a session must belong to the same Google Cloud Console project. Once a session has concluded, the token is no longer valid; your app must generate a fresh token for each session. If the sessionToken parameter is omitted, or if you reuse a session token, the session is charged as if no session token was provided (each request is billed separately). Note: Address Validation can only be used in sessions with the Autocomplete (New) API, not the Autocomplete API. See https://developers.google.com/maps/documentation/places/web-service/session-pricing for more details.