This error will appear when the Header/Sender Id passed by you with the SMS is not added along with the associated Template on the DLT platform.
You might be making one of the below mistakes:
1. While applying Template on DLT, you have not added this Header with the Template.
2. This Header is not even approved in your DLT account.
3. This Header is applied by you after applying this Template
Now, you need to log in to the DLT platform and edit your approved Template by associating it with the Header you want to send SMS with.
How to EDIT Template on PingConnect:
1. Go to the Template section in the left menu and click on the EDIT button against that Template:
2. Select the Header you want to associate with that Template or click on select all: