As per this official Document :

If you get this error, do the following :

• Make sure you've enabled the Pub/Sub API in the Google Cloud console.

• Make sure that the principal making the request has the required permissions on the relevant Pub/Sub API resources, especially if you

  are using Pub/Sub API for cross-project communication.

• If you're using Dataflow, make sure that both {PROJECT_NUMBER}@cloudservices.gserviceaccount.com and the Compute

  Engine Service account

  {PROJECT_NUMBER}[email protected] have the

  required permissions on the relevant Pub/Sub API resource. For more

  information, see Dataflow Security and Permissions.

• If you're using App Engine, check your project's Permissions page to see if an App Engine Service Account is listed as a Pub/Sub Editor. If it is not, add your App Engine Service Account as a Pub/Sub Editor. Normally, the App Engine Service Account is of the form <project-id>@appspot.gserviceaccount.com.

Refer to this document for more information and go through this stack link which might be helpful for you.