Issue connecting pub/sub from PCF - spring-boot

Question

I'm trying to connect google Pub/Sub from PCF environment(Spring boot app). The app is successfully loaded the credentials from credentials.json file and it printed Project ID. but it is printing below error after started.
c.g.a.oauth2.ComputeEngineCredentials : Failed to detect whether we are running on Google Compute Engine.
ERROR 13 --- [nio-8080-exec-4] o.a.c.c.C.[.[.[/].[dispatcherServlet] : Servlet.service() for servlet [dispatcherServlet] in context with path [] threw exception [Request processing failed; nested exception is java.lang.IllegalStateException: Expected the service InnerService [FAILED] to be RUNNING, but the service has FAILED] with root cause
java.io.IOException: The Application Default Credentials are not available. They are available if running in Google Compute Engine. Otherwise, the environment variable GOOGLE_APPLICATION_CREDENTIALS must be defined pointing to a file defining the credentials. See https://developers.google.com/accounts/docs/application-default-credentials for more information.
Here is the code which I'm using and I'm invoking this method from a sample rest controller.
public static void subscribeAsyncExample(String projectId, String subscriptionId) {
ProjectSubscriptionName subscriptionName =
ProjectSubscriptionName.of(projectId, subscriptionId);
System.out.println("Processing messages...");
MessageReceiver receiver =
(message, consumer) -> {
System.out.println("Id : " + message.getMessageId());
System.out.println("Data : " + message.getData().toStringUtf8());
consumer.ack();
};
Subscriber subscriber = null;
try {
subscriber = Subscriber.newBuilder(subscriptionName, receiver).build();
subscriber.startAsync().awaitRunning();
subscriber.awaitTerminated();
} finally {
if (subscriber != null) {
subscriber.stopAsync();
}
}
}
pom.xml
Spring boot: 2.3.2.RELEASE
spring-cloud-gcp.version: 1.1.3.RELEASE
`
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-gcp-starter-pubsub</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
</dependency>
<dependency>
<groupId>com.google.cloud</groupId>
<artifactId>google-cloud-pubsub</artifactId>
</dependency>
<dependency>
<groupId>com.google.cloud</groupId>
<artifactId>google-cloud-storage</artifactId>
</dependency>
`
Log:
The default project ID is *******
Default credentials provider for service account *****-client-account#*******.gserviceaccount.com
Scopes in use by default credentials: [https://www.googleapis.com/auth/pubsub, https://www.googleapis.com/auth/trace.append, https://www.googleapis.com/auth/spanner.admin, https://www.googleapis.com/auth/cloudruntimeconfig, https://www.googleapis.com/auth/sqlservice.admin, https://www.googleapis.com/auth/devstorage.read_only, https://www.googleapis.com/auth/devstorage.read_write, https://www.googleapis.com/auth/cloud-platform, https://www.googleapis.com/auth/spanner.data, https://www.googleapis.com/auth/datastore, https://www.googleapis.com/auth/cloud-vision]