- Missing sender address - select the sender address to use for the campaign. If you don't have any in the selection list it means none of the addresses you have added have been verified. Go to menu Profile / My account / Emails to add a new address and verify it's existence.
- Misconfigured A/B test - both versions of A/B test must have an email address selected and the subject line entered.
- Insufficient credit - go to menu Profile / Payments / Buy credit and get the required amount of credit for your campaign.