Same issue – I received an email with subject: “URL: Post SMTP email error” from your plugin with the following error:
You getting this message because an error detected while delivered your email.
For the domain: [URL removed]
The log to paste when you open a support issue:
Code: 400, Message: Bad Request, Body: {“errors”:[{“message”:”Invalid type. Expected: array, given: object.”,”field”:”personalizations”,”help”:”http://sendgrid.com/docs/API_Reference/Web_API_v3/Mail/errors.html#-Personalizations-Errors”}]}