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Please hold on to use the Java SDK with A2P methods directly as we are updating the specs which may cause code breaks later.

For now, I recommended to use the post() and get() method directly with specified endpoint and params.

public ResponseBody get(String endpoint, Object queryParameters) throws IOException, RestException {
    return request(HttpMethod.GET, endpoint, queryParameters, null);
}
public ResponseBody post(String endpoint, Object object) throws IOException, RestException {
    return request(HttpMethod.POST, endpoint, null, object, ContentType.JSON);
}

E.g.

public class Filters {
        public String view = "";
        public String dateFrom = "";
        public String dateTo = "";
}
/*
Other valid filters
    perPage: integer
    batchId: string
    direction: Array
    phoneNumber: Array
*/

public void read_a2p_message_store() {
    var params = new Filters();
    params.view = "Detailed";
    params.dateFrom = "2020-11-20T00:00:00.000Z";
    params.dateTo = "2020-11-30T00:00:00.000Z";

    ResponseBody resp = restClient.get("/restapi/v1.0/account/~/a2p-sms/messages", params);
    System.out.println(resp.string());
}

We will update the SDK as soon as we can.