refactor: improve error handling for email sending failures

client/create.go

@@ -40,7 +40,14 @@ func (client *Client) SendEmail(request *EmailRequest) (*EmailCreateResponse, er
 	if resp.StatusCode >= http.StatusBadRequest {
 		response, err := readResponseBody[Response[ErrorResponse]](resp)
 		if err != nil {
-			return nil, err
+			bodyContents := make([]byte, resp.ContentLength)
+			_, err := resp.Body.Read(bodyContents)
+
+			if err != nil {
+				return nil, errors.New("Failed to read error response body: " + err.Error())
+			}
+
+			return nil, errors.New("An error occurred while sending the email: " + resp.Status + " - " + string(bodyContents))
 		}
 
 		if response.Payload.Message == "" {