Error : Mailjet API v1
If you're a long time customer, you'll may have the Version 1 API. DeliPress needs the version 3. You must ask a migration to the Mailjet support team.
Mailchimp – Your Campaign is not ready to send
Error MailChimp : Your Campaign is not ready to send.
SendinBlue – Unable to send test email
If you can't send a test email with SendinBlue, it's because you must add the email address as subsrcriber to one of your lists.
WordFence – Create a campaign
You can't send your campaign and you are using WordFence.
Sendgrid – Unable to send test
If you can't send a test email with SendGrid, it's because you need to configure your email as sender in SendGrid app online.