GCP TSE is here to help you with your situation 🤞.

1. How can I restore the <number>[email protected] account?

You're right - as per Google Cloud Docs [1] you can't restore your Service Account (SA), because after 30 days, IAM permanently removes it.

2. How can I configure the Firebase CLI to use a newly created or existing service account for Cloud Functions deployment instead of the deleted default?

Firebase CLI has several ways [2] to authenticate to API: using the Application Default Credentials (ADC) or using FIREBASE_TOKEN (considered legacy). You might have some kind of custom setup, but in general to authenticate Firebase CLI with a SA you should follow this simple guide [3]:

1. Locate an existing SA or create a new one to be used by Firebase CLI;
2. Grant all required roles to this SA (explained in [3], but you might need more narrow roles for your specific case);
3. Setup ADC depending on your environment;
4. Update the GOOGLE_APPLICATION_CREDENTIALS OS environment variable using gcloud auth application-default login or manually (depending on your dev environment). Details are in the linked docs.

[1] https://cloud.google.com/iam/docs/service-accounts-delete-undelete#undeleting
[2] https://firebase.google.com/docs/cli#cli-ci-systems
[3] https://firebase.google.com/docs/app-distribution/authenticate-service-account
[4] https://cloud.google.com/docs/authentication/provide-credentials-adc

If you haven't solved your problem using the above guide, please explain your deployment process stp-by-step. Also, try to answer as much as possible:

• What you're inserting as a value for the `KEY_FILE' key?
• Are you using both KEY_FILE and FIREBASE_TOKEN keys simultaneously?
• Are you using the PROJECT_ID key?