When sending an AlimTalk message if your message delivery failed with an error code 3015, check when the AlimTalk template you used was last used.
This error code can indicate that the AlimTalk template has became dormant. When a template has not been used more than one month, KakaoTalk will move the template into a dormant state. If you find that this template was last used more than a month ago, then you can contact Sinch customer support. Ask support to activate the template again by providing them with the template code, KakaoTalk Business Channel ID and your Sinch account details.
Alternatively, you can create a new AlimTalk template with a different template code.