To check if an approved SMS template works as transactional,

Copy the template,

Click on the SMS button on the top right,

type in a DND number (Check if that number is a DND number)

paste the template in the SMS body
Replace all occurrences of %s (if any) with any set of alpha numeric characters, something like this: rgb567kjb

and click send.

If the DND number receives the SMS, then the template is working fine.