This occurs because, during the trial period, your content is automatically replaced with that message. To comply with regulations, you will need to purchase a number and verify your use case in order to send your own content. You can download the necessary form here, and we'll assist you in obtaining a Toll-Free number. Once you have it, you'll be able to send your content freely.
For further assistance, do raise a support ticket with our Support Team at support@moceanapi.com.