I want to use the API services from my java application

I want to use the API services from my java application.

I tried adding the dependency in my POM.xml file, but it is not in the maven repository.

So I downloaded the java SDK from Git, compiled it and imported the .jar file into my Maven library, that way I don't get any compilation errors.

add the code as it is in the "Read me" file, to the code in my application.

import com.telstra.ApiClient;
import com.telstra.ApiException;
import com.telstra.Configuration;
import com.telstra.auth.OAuth;
import com.telstra.messaging.*;

ApiClient defaultClient = Configuration.getDefaultApiClient();
defaultClient.setBasePath("https://tapi.telstra.com/v2");

// Configure OAuth2 access token for authorization
OAuth auth = (OAuth) defaultClient.getAuthentication("auth");
AuthenticationApi authenticationApi = new AuthenticationApi(defaultClient);
String clientId = "XYZ";
String clientSecret = "ABC";
String grantType = "client_credentials";
String scope = "NSMS";
try {
    OAuthResponse oAuthResponse = authenticationApi.authToken(clientId, clientSecret, grantType, scope);
    auth.setAccessToken(oAuthResponse.getAccessToken());
} catch (ApiException e) {
    System.err.println("Exception when calling AuthenticationApi#authToken");
    System.err.println("Status code: " + e.getCode());
   System.err.println("Reason: " + e.getResponseBody());
    System.err.println("Response headers: " + e.getResponseHeaders());
    e.printStackTrace();
}

But directly in the first line:

ApiClient defaultClient = Configuration.getDefaultApiClient();

get an exception error:

java.lang.NoClassDefFoundError: Could not initialize class com.telstra.Configuration

Clearly I am doing something wrong.

Can you help me, or give me a video or tutorial on how to integrate the API in my java application?