The easiest way is to fix using gcloud cli. More docs here https://cloud.google.com/pubsub/docs/quickstart-cli#before-you-begin

install gcloud

sudo apt-get install google-cloud-sdk

then call

gcloud init

then check your active project and credentials

gcloud config configurations list

If it is not ok, make sure you are authenticated with the correct account:

gcloud auth list
* account 1
  account 2

Change to the project’s account if not:

gcloud config set account `ACCOUNT`

Depending on the account, the project list will be different:

gcloud projects list

- project 1
- project 2...

Switch to intended project:

gcloud config set project `PROJECT NAME`

Then Create Application Default Credentials with gcloud auth application-default login, and then google-cloud will automatically detect such credentials.