If you are using OneAPI (Send SMS via Flow) of MSG91 (https://api.msg91.com/api/v5/flow/), you do not need to bother your developer; you just need follow below steps
1. Login to the MSG91 panel
2. Go to the OneAPI section
3. Click on the Edit button against your Template
4. Add the DLT Template Id against the DLT approved Template.
5. Save the Template and then click on the Test DLT button against your Template.
6. Now, check your phone for this SMS; if you have received this SMS, that means that this Template, Header, and Template Id combination will work in the right way once the DLT Template is LIVE.
7. If you have not received this SMS, login to the MSG91 panel, go to the logs section, and search for this particular number. You will be able to see the exact reason for failure when you bring the cursor on the red failure sign.
8. Based on the failure reason, correct your mistake and try again.
MSG91 will forward this DLT Template Id to Telecom Operators if you submit SMS through that Flow.
API Doc- https://docs.msg91.com/collection/msg91-api-integration/5/send-sms-via-flow/T29N6CRT
Help Doc- https://msg91.com/help/how-to-create-flow-id-to-send-sms-via-api