If MailBluster is still giving a message to move out of sandbox, the issue is usually linked to your Amazon SES account. To fix this, you can simply refresh the Amazon SES usage box as shown below:

But if it wasn’t updated, then most of the time, the reason is that Amazon SES moved you out of the sandbox in a different region (not the one that you have selected). The confirmation email should contain the Region; please choose the same region on MailBluster.
If the issue still persists, then generate the AWS Credentials again correctly by following this video tutorial: