Truecaller app allows you to manage calls as well as send and receive text messages.
And to use it you need to enable particular permissions, only then you can send messages.
If you don’t allow the application to access messages then you will find “Not Sent” text written below the SMS.
There are some other TrueCaller users who have reported that their texts are sent but not delivered to the recipient.
But in some cases, the TrueCaller settings configuration is blamed for this problem.
Whether it is your app or your smartphone is causing this problem, you can fix messages not sent or delivered on Truecaller easily by following the solutions discussed in this troubleshooting guide.