Contact the administrator of your account for additional permissions.
Make sure you've entered the proper email address. If the email address was correct, describe your problem to our support center.
Check the access scope of the given API key. The API key menu is available here. To add an API key, you need to specify the name, audience, scope, and roles.
Whenever you receive that error, the error indicates that the selected email templates do not contain one of required data inserts (Jinjava tag) that is mentioned in this article.
In case of OAuth authentication, an HTTP400 error is usually the result of incorrect data mapping. If this is the source of the issue, under the message key there will be information such as "Key email not found in oauth data", and usually it means that the response from the endpoint you have configured did not contain that key.
In all other cases, verify input data coming from your application.