Approved Emails are not being delivered. The Send Email record has a Status = Failed with Status Details = Failed to connect to Vault for validation.
The Vault integration user login access expired. Or, the user does not have the correct API access in Vault.
The Vault Integration User must be assigned to a Vault Security Policy (Navigate to: Users --> Settings --> Security Policy) that has a Password Expiration value of No Expiration. If the password ever expires, the integration fails.
Ensure that the Security Profile allows the Integration access to all the fields and document types. The user needs API access to all API and, at least, Read access to Document Fields and Document Types. The user can be set to the System Admin Security Profile or a Custom Profile with these settings.