Enum describing possible identity verification errors.

[Proto definition ![GitHub](https://developers.google.com/site-assets/logo-github.svg)](https://github.com/googleapis/googleapis/blob/master/google/ads/googleads/v26/errors/identity_verification_error.proto)

| Enums ||
|---|---|
| ## `BILLING_NOT_ON_MONTHLY_INVOICING` | Customer is not on monthly invoicing. |
| ## `NO_EFFECTIVE_BILLING` | No effective billing linked to this customer. |
| ## `UNKNOWN` | The received error code is not known in this version. |
| ## `UNSPECIFIED` | Enum unspecified. |
| ## `VERIFICATION_ALREADY_STARTED` | Verification for this program type was already started. |