Secrets.toml not Found

It should look something like this (in toml format)

[gcp_service_account]

type = "service_account"
project_id = "PROJECT_ID"
private_key_id = "KEY_ID"
private_key = "-----BEGIN PRIVATE KEY-----\nPRIVATE_KEY\n-----END PRIVATE KEY-----"
client_email = "SERVICE_ACCOUNT_EMAIL"
client_id = "CLIENT_ID"
auth_uri = "https://accounts.google.com/o/oauth2/auth"
token_uri = "https://accounts.google.com/o/oauth2/token"
auth_provider_x509_cert_url = "https://www.googleapis.com/oauth2/v1/certs"
client_x509_cert_url = "https://www.googleapis.com/robot/v1/metadata/x509/SERVICE_ACCOUNT_EMAIL"

You can see more info about creating and using those credentials here Create and manage service account keys  |  IAM Documentation  |  Google Cloud