If the request is successful, it will contain an empty response.
If the request is not successful because of invalid attributes, an
attributes_error dictionary will be included in the response with additional details as to which attributes could not be saved and why (see the example 400 response for an example error body).
Attribute Key Restrictions
For a full list of reserved attribute keys and restrictions refer to the Subscriber Attributes guide here. To send reserved attribute keys, prefix the key with